ANDROID: drm/virtio: stop using drv->context when creating fence

The plumbing is all here to do this.  Since we always use the
default fence context when allocating a fence, this makes no
functional difference.

We can't process just the largest fence id anymore, since it's
it's associated with different timelines.  Process each fence_id
individually.

Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>

BUG: 173630595
TEST: boot VM

Change-Id: I951436ba707a98ce826dfa467e1ed5f1cded97e1