radv: add a missing async compute workaround for Tonga/Iceland

radv: add a missing async compute workaround for Tonga/Iceland

After digging into PAL code again, I figured that Tonga/Iceland are
both affected by a hw bug related to async compute dispatches.

The solution is to change the "threadgroup" dimension mode to the
"thread" dimension mode unconditionally.

This should fix a bunch of issues related to RADV_DEBUG=nocompute on
these GPUs.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/7551
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/6334
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/4679
Cc: mesa-stable
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26207>
(cherry picked from commit ec82b4294432aa6da40517655a4f8af2767176a2)