drm/i915/dvo: Use intel_de_rmw() for DVO enable/disable

Replace the hand rolled RMW with intel_de_rmw() in the DVO
port enable/disable functions. Also switch to intel_de_posting_read()
for the posting read (though maybe it should be just be nuked...).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221122120825.26338-9-ville.syrjala@linux.intel.com


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