drm/i915/lvds: Use intel_de_rmw()

Replace the hand rolled rmw stuff with intel_de_rmw().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230130180540.8972-3-ville.syrjala@linux.intel.com


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