drm/nouveau: make sure display hardware is reinitialised on runtime resume

Linus commit 05c63c2ff23a80b654d6c088ac3ba21628db0173 modified the
runtime suspend/resume paths to skip over display-related tasks to
avoid locking issues on resume.

Unfortunately, this resulted in the display hardware being left in
a partially initialised state, preventing subsequent modesets from
completing.

This commit unifies the (many) suspend/resume paths, bringing back
display (and fbcon) handling in the runtime paths.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>