drm/nvc0: enable protection of system-use-only structures in vm

Somehow missed this in the original merge of the nvc0 code.

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

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

diff --cc drivers/gpu/drm/nouveau/nv50_instmem.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nvc0_graph.c
Simple merge

diff --cc drivers/gpu/drm/nouveau/nvc0_vm.c
Simple merge