drm/i915: Extract intel_edp_has_drrs()

Pull all the eDP specific platform/port checks out from
intel_drrs_init() into intel_edp_has_drrs().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220331112822.11462-2-ville.syrjala@linux.intel.com


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