drm: Add FEC registers for LT-tunable repeaters

FEC is supported since DP 1.4, and it was expanded for LT-tunable in DP
1.4a. This commit adds the address registers for
FEC_ERROR_COUNT_PHY_REPEATER1 and FEC_CAPABILITY_PHY_REPEATER1.

Cc: Abdoulaye Berthe <Abdoulaye.Berthe@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Abdoulaye Berthe <Abdoulaye.Berthe@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: Zhan Liu <zhan.liu@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191205135856.232784-1-Rodrigo.Siqueira@amd.com

include/drm/drm_dp_helper.h

@@ -1042,6 +1042,8 @@
 #define DP_SYMBOL_ERROR_COUNT_LANE2_PHY_REPEATER1	    0xf0039 /* 1.3 */
 #define DP_SYMBOL_ERROR_COUNT_LANE3_PHY_REPEATER1	    0xf003b /* 1.3 */
 #define DP_FEC_STATUS_PHY_REPEATER1			    0xf0290 /* 1.4 */
+#define DP_FEC_ERROR_COUNT_PHY_REPEATER1                    0xf0291 /* 1.4 */
+#define DP_FEC_CAPABILITY_PHY_REPEATER1                     0xf0294 /* 1.4a */
 
 /* Repeater modes */
 #define DP_PHY_REPEATER_MODE_TRANSPARENT		    0x55    /* 1.3 */