radeonsi: force dcc clear to use compute clear

radeonsi: force dcc clear to use compute clear

After the previous commit, when running the following
deqp-gles31 caselist:

  dEQP-GLES31.functional.image_load_store.2d.format_reinterpret.rgba32f_rgba32ui
  dEQP-GLES31.functional.image_load_store.2d.format_reinterpret.rgba32f_rgba32i

The second test always fails on gfx10. I don't know why,
but forcing the dcc clear from si_decompress_dcc to use
compute fixes the problem.

The test caselist wasn't failing before because the dcc
disable step was done in si_resource_copy_region, before
calling si_compute_copy_image.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8958>