Android Things with Rasp3 7 inch touchscreen

You can try to manually mount the boot partition from the sdcard and edit config.txt

mount -t msdos /dev/sdX1 /mnt/disk
echo 'lcd_rotate=2' >> /mnt/disk/config.txt

Where /dev/sdX1 points to your sdcard reader device.

Note: This is more a hack than an officially supported solution, you will have to re-do that operation everytime you upgrade the OS image. It'd be nice to file a feature request to ask for better support for (dynamic?) display configuration