drm/nouveau: fix fbcon not being accelerated after suspend

This does *not* (and is not intended to) fix the issue reported by
Christoph Rudorff on the nouveau mailinglist.

The patch proposed (which is similar to this one, but also reorders
whether we disable accel or call fb_set_suspend first), papers over
another problem entirely by avoiding touching the framebuffer.

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