drm/i915: Extract can_enable_drrs()

Pull the "can we do DRRS?" check into helper in order
to reduce the clutter in intel_drrs_compute_config().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220128103757.22461-12-ville.syrjala@linux.intel.com


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