drm/nvc0: fix suspend/resume of PGRAPH/PCOPYn

We need the physical VRAM address in vinst, even for objects mapped into
a vm, as the gpuobj suspend/resume code uses PMEM to access the object.

Previously, vinst was overloaded to mean "VRAM address" for !VM objects,
and "VM address" for VM objects, causing the wrong data to be accessed
during suspend/resume.

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