drm/i915: Make utility pin asserts more accurate

Only the PWM output mode of the utility pin is incompatible
with DC6/LCPLL disable. Check for that specifically.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/6609


Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230328164938.8193-1-ville.syrjala@linux.intel.com


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