Could dark matter consist of the supermassive black holes at the centers of galaxies?

Do the black holes at the center of galaxies account for the experimental results that prompted the introduction of dark matter? No

The primary piece of evidence that originally sparked the idea of dark matter is the rotation curve of galaxies. We found that galaxies don't rotate like the luminous matter suggests it should rotate. Specifically, given some estimates of enclosed mass at some radius from the center of a given galaxy, galaxies were found to rotate faster at given radii than expected. In other words, the luminous matter didn't seem to account for all the mass within any given radius. This lead to the idea that galaxies are permeated by a "dark matter" that isn't luminous. For this idea to work though, the dark matter needs to permeate the galaxy, it can't all be concentrated at the center of the galaxy like the central black hole (to really explain why this is one would have to get into a bit more details into rotation curves and how the expectations differ from observations).

Other pieces of evidence, like the dynamics which occurs when two galactic clusters collide also wouldn't be accounted for by galactic central black holes. See e.g. the bullet cluster.

Is it possible that the dark matter is made up of many smaller black holes? Possible, but not likely.

At one point in time, there was conjecture that the dark matter consisted of (moderate sized) black holes and other compact objects which have low luminosity. This was the MACHO theory (MAssive Compact Halo Objects). But this theory has largely fallen out of favor.

As Ben points out in a comment, another candidate might be primordial black holes, but their abundance appears to be too low to be good candidates at this time.

Black holes don't have "infinite gravity". The only "infinite thing" associated with a black hole is that the value of the Riemann curvature tensor at the center of a (Schwarzschild or Reissner-Nordstrom) black hole is infinity according to general relativity. But we know that general relativity is not supposed to be a reliable theory near the center of the black hole (where the quantum gravity effects presumably take over)--and thus, even this single infinitely large quantity that we can associate with a black hole is also not really reliably infinite.

Anyway, even if the curvature were infinitely large at the center of the black hole, the effects of gravitation of the black hole are always finite at every point (inside and outside of the black hole) except for the center itself. In fact, according to the Birkhoff theorem (for spherically symmetric stationary black holes), the gravitational effects outside the event horizon cannot be identified as any different from the same of an equally massive spherically symmetric non-black object (which would be centered at the center of the black hole)! So, for example, if the Sun collapsed to a black hole, the Earth (or Mercury or anything outside the surface of the Sun) wouldn't feel a thing as far as the gravitational effects are concerned. So, there is no such thing as "an infinite gravity of a black hole".

Now, dark matter is supposed to be distributed throughout the galaxy. There might be some density distribution I suppose but all of dark matter isn't centered at the center of the galaxy. If it were, we wouldn't find anomalies in the galactic rotation curves which led us to postulate dark matter in the first place! So, no, dark matter (at least that we observe throughout the galaxy) cannot be just some effect due to the black hole at the center of the galaxy.

This galaxy rotation simulation from Wikipedia explains pretty well how the concept of the dark matter came into existence. Your assumption that the mass of a galaxy belongs to the baryonic matter and the central black hole corresponds to the left video, where stars closer to the galaxy centre rotate faster than the ones on the periphery. What the astronomers actually observe is similar to the right video, where the orbital speed of the stars doesn't change much, or even slightly increases with distance from the centre of a galaxy.

The observed rotation curves suggest that the total mass of a galaxy is distributed differently from its observable mass, even including the black holes. Furthermore, adjusting the estimated mass of the central black hole changes absolute orbital speeds, not the relationship between orbital speeds and radial distances. Dark matter is a concept which was introduced primarily to account for this discrepancy between observations and simulations, which could not be explained with observable objects alone.