r600g/compute: Emit DEALLOC_STATE on cayman after dispatching a compute shader.

r600g/compute: Emit DEALLOC_STATE on cayman after dispatching a compute shader.

This is necessary to prevent the next SURFACE_SYNC packet from
hanging the GPU.

https://bugs.freedesktop.org/show_bug.cgi?id=73418

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
CC: "9.2" "10.0" <mesa-stable@lists.freedesktop.org>