drm/i915/dpio: Use intel_de_rmw() for BXT DPIO latency optim setup

Replace the hand rolled intel_de_rmw() with the real thing.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240412175818.29217-6-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>