drm/i915: Use intel_dp_has_dsc() during .compute_config()

Reuse intel_dp_has_dsc() during .compute_config() instead of
repeating some of the checks again by hand. We'll be adding
more checks to intel_dp_has_dsc() and this will make sure
we cover both .mode_valid() and .compute_config() with them.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240517145356.26103-5-ville.syrjala@linux.intel.com


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