drm/dp: Add drm_dp_fast_training_cap() helper

Add a helper that checks for the fast training capability given the DPCD
receiver capabilities blob.
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191021143437.1477719-4-thierry.reding@gmail.com

include/drm/drm_dp_helper.h

@@ -1215,6 +1215,13 @@ drm_dp_enhanced_frame_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 		(dpcd[DP_MAX_LANE_COUNT] & DP_ENHANCED_FRAME_CAP);
 }
 
+static inline bool
+drm_dp_fast_training_cap(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
+{
+	return dpcd[DP_DPCD_REV] >= 0x11 &&
+		(dpcd[DP_MAX_DOWNSPREAD] & DP_NO_AUX_HANDSHAKE_LINK_TRAINING);
+}
+
 static inline bool
 drm_dp_tps3_supported(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 {