drm/nouveau: Use drm_fb_helper_fill_info

This changes the fb name from "nouveaufb" to "nouveaudrmfb".

Aside: I wonder whether the in_interrupt() check is good enough for
the nouveau acceleration. Cargo-cult says drm_can_sleep() is needed,
which isn't actually working if you pick a .config without PREEMPT.
For the generic fbdev defio support we've gone with offloading
everything to a worker. For the non-accel callbacks (set_par, blank
and friends) checking for oops_in_progress is good enough to catch all
the evil calling contexts.

v2: Rebase

Acked-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: nouveau@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20190326132008.11781-14-daniel.vetter@ffwll.ch