drm/vmwgfx: takedown vram manager

Don't bother returning EBUSY, nobody cares enough,
if the driver has a problem, it should deal with it.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200804025632.3868079-29-airlied@gmail.com