drm: Add LT-tunable PHY repeater mode operations

LT-tunable PHY Repeaters can operate in two different modes: transparent
(default) and non-transparent. The value 0x55 specifies the transparent
mode, and 0xaa represents the non-transparent; this commit adds these
two values as definitions.

Cc: Abdoulaye Berthe <[e-mail]>
Cc: Harry Wentland <[e-mail]>
Cc: Leo Li <[e-mail]>
Cc: Jani Nikula <[e-mail]>
Cc: Manasi Navare <[e-mail]>
Cc: Ville Syrjälä <[e-mail]>
Signed-off-by: Abdoulaye Berthe <[e-mail]>
Signed-off-by: Rodrigo Siqueira <[e-mail]>
Reviewed-by: Ville Syrjälä <[e-mail]>
Reviewed-by: Harry Wentland <[e-mail]>
Signed-off-by: Rodrigo Siqueira <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

include/drm/drm_dp_helper.h

···
 #define DP_SYMBOL_ERROR_COUNT_LANE3_PHY_REPEATER1	    0xf003b /* 1.3 */
 #define DP_FEC_STATUS_PHY_REPEATER1			    0xf0290 /* 1.4 */
 
+/* Repeater modes */
+#define DP_PHY_REPEATER_MODE_TRANSPARENT		    0x55    /* 1.3 */
+#define DP_PHY_REPEATER_MODE_NON_TRANSPARENT		    0xaa    /* 1.3 */
+
 /* DP HDCP message start offsets in DPCD address space */
 #define DP_HDCP_2_2_AKE_INIT_OFFSET		DP_HDCP_2_2_REG_RTX_OFFSET
 #define DP_HDCP_2_2_AKE_SEND_CERT_OFFSET	DP_HDCP_2_2_REG_CERT_RX_OFFSET