drm/vmwgfx: Implement SOU plane update for BO backed fb

Using the new interface implement SOU plane update for BO backed fb.

v2: Rebase to new resource validation.

Signed-off-by: Deepak Rawat <drawat@vmware.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>