drm/nouveau/pm: improve memtiming mappings

Improvements:
 - Fix bug in switch statement
 - Add parts of 0x10022c, 0x10023c
 - Clean up 0x100234
 - Comment out assumption in 0x100228 until verified

Signed-off-by: Roy Spliet <r.spliet@student.tudelft.nl>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>