r600/sfn: always use four slots for Cayman trans ops

r600/sfn: always use four slots for Cayman trans ops

This is a partial revert of
  ed6204eb0 (r600/sfn: only use 3 channels on Cayman for trans ops)

The scheduler and/or optimizer passes generate faulty code when
we use only three slots as decribed in the spec. So for now disable
this optimization.

Fixes: ed6204eb0 (r600/sfn: only use 3 channels on Cayman for trans ops)
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/7774

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20034>