drm/i915/de: Replace __intel_de_rmw_nowl() with intel_de_rmw_fw()

drm/i915/de: Replace __intel_de_rmw_nowl() with intel_de_rmw_fw()

We already have the lower level intel_de_*_fw() stuff, so use
that instead of hand rolling something custom for the DMC
wakelock stuff.

As the wakelock stuff exists only on platforms supported
by the xe driver this doesn't even result in any functional
changes since xe doesn't have uncore.lock nor unclaimed
register access detection.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/20251110172756.2132-13-ville.syrjala@linux.intel.com
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>