drm/nouveau/mmu: switch to instanced constructor

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>

drm/nouveau/mmu/mcp77: fix regressions in stolen memory handling

- Fixes addition of stolen memory base address to PTEs.
- Removes support for compression.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Tested-by: Pierre Moreau <pierre.morrow@free.fr>