drm/gk104/gr: disable PGOB at init time

This removes the previous hack that worked on some boards.

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

diff --cc drivers/gpu/drm/nouveau/core/engine/graph/gk20a.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/core/engine/graph/nve4.c
Simple merge