radeonsi: don't use SQC_CACHES to flush ICACHE and KCACHE on SI

radeonsi: don't use SQC_CACHES to flush ICACHE and KCACHE on SI

This reverts 73c2b0d18c51459697d8ec194ecfc4438c98c139.

It doesn't seem to be reliable. It's probably missing a wait packet or
something, because it's just a register write and doesn't wait for anything.
SURFACE_SYNC at least seems to wait until the flush is done. Just guessing.

Let's not complicate things and revert this.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88561

Cc: 10.5 <mesa-stable@lists.freedesktop.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>