drm/dp: Add drm_dp_128b132b_supported()

Factor out a function to check for 128b/132b channel coding support used
by a follow-up patch in the patchset.

v2: s/drm_dp_uhbr_channel_coding_supported()/drm_dp128b132b_supported()
    (Jani)

Cc: dri-devel@lists.freedesktop.org
Cc: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Manasi Navare <navaremanasi@chromium.org>
Acked-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240417141936.457796-1-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_dp.c

@@ -225,7 +225,7 @@ static void intel_dp_set_dpcd_sink_rates(struct intel_dp *intel_dp)
 	 * Sink rates for 128b/132b. If set, sink should support all 8b/10b
 	 * rates and 10 Gbps.
 	 */
-	if (intel_dp->dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_128B132B) {
+	if (drm_dp_128b132b_supported(intel_dp->dpcd)) {
 		u8 uhbr_rates = 0;
 
 		BUILD_BUG_ON(ARRAY_SIZE(intel_dp->sink_rates) < ARRAY_SIZE(dp_rates) + 3);

include/drm/display/drm_dp_helper.h

@@ -251,6 +251,12 @@ drm_dp_channel_coding_supported(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 	return dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_8B10B;
 }
 
+static inline bool
+drm_dp_128b132b_supported(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	return dpcd[DP_MAIN_LINK_CHANNEL_CODING] & DP_CAP_ANSI_128B132B;
+}
+
 static inline bool
 drm_dp_alternate_scrambler_reset_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 {