Can't use "userspace" cpufreq governor and set cpu frequency

This is because your system is using the new driver called intel_pstate. There are only two governors available when using this driver: powersave and performance.
The userspace governor is only available with the older acpi-cpufreq driver (which will be automatically used if you disable intel_pstate at boot time; you then set the governor/frequency with cpupower):

• disable the current driver: add intel_pstate=disable to your kernel boot line
• boot, then load the userspace module: modprobe cpufreq_userspace
• set the governor: cpupower frequency-set --governor userspace
• set the frequency: cpupower --cpu all frequency-set --freq 800MHz