drm/i915: Move PIPE_CHICKEN RMW out from the vblank evade critical section

drm/i915: Move PIPE_CHICKEN RMW out from the vblank evade critical section

We don't want any RMWs in the part of the commit that happens
under vblank evasion. Eventually we want to use the DSB to
handle that and it can't read registers at all. Also reads
are just slowing us down needlessly.

Let's move the whole PIPE_CHICKEN stuff out from the critical
section since we don't have anything there that needs to be
syncrhonized with other plane/pipe registers. If we ever need
to add such things then we have to move it back, but without
doing any reads.

TODO: should look into eliminating the RMW anyway...

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220202111616.1579-1-ville.syrjala@linux.intel.com
Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>