drm/nouveau/kms: take more care when pulling down accelerated fbcon

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

diff --cc drivers/gpu/drm/nouveau/dispnv04/crtc.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nouveau_fbcon.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nouveau_fbcon.h
Simple merge