We need to synchronize across rings when doing a bo move to make
sure we the buffer is idle if it's in use by a different ring than
the ring doing the move.

v2: fix fence setup for bo moves

v3: add missing ring lock/unlock
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>