radeonsi/compute: Let the state tracker do all the flushing

radeonsi/compute: Let the state tracker do all the flushing

It shouldn't be necessary to call radeon_winsys::cs_flush() from
radeonsi_launch_grid(), because the state tracker is responsible for
flushing the pipeline at the appropriate time.  The current behavior is
also wrong, because radeonsi_launch_grid() submits packets to the
compute ring, but when the state tracker calls pipe->flush() everything
is submitted to the graphics ring.  This has the potential to create a
race condition.

The downside of removing this flush is that the compute dispatch packets
will be sent to the graphics ring rather than the compute ring.
In the future we will need to come up with a way to detect 'compute'
command streams and submit them to the appropriate ring.

Signed-off-by: Marek Olšák <marek.olsak@amd.com>