drm/nouveau: remove ability to use external firmware

This was always really a developer option, and if it's really necessary we
can hack this in ourselves.

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

diff --cc drivers/gpu/drm/nouveau/Makefile
Simple merge

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

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

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

diff --cc drivers/gpu/drm/nouveau/nv40_graph.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nv50_graph.c
Simple merge