drm/nv50-nvc0/vm: support unsnooped system memory

v2 (Emil Velikov <emil.l.velikov@gmail.com>):
- Fixed a regression on certain nv50 IGP due to not passing the correct
  target type to nv50_vm_addr()

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Tested-by: Johannes Obermayr <johannesobermayr@gmx.de>

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

diff --cc drivers/gpu/drm/nouveau/nv50_vm.c
Simple merge

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