drm/amd/display: expand the non standard link rate for testing

[Why]
6.75 Gbps link rate training for DP_TEST_LINK_RATE_RATE_8
Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Allen Pan <allen.pan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dc_dp_types.h

@@ -137,8 +137,13 @@ enum dp_link_encoding {
 
 enum dp_test_link_rate {
 	DP_TEST_LINK_RATE_RBR		= 0x06,
+	DP_TEST_LINK_RATE_RATE_2    = 0x08,	// Rate_2        - 2.16 Gbps/Lane
+	DP_TEST_LINK_RATE_RATE_3    = 0x09,	// Rate_3        - 2.43 Gbps/Lane
 	DP_TEST_LINK_RATE_HBR		= 0x0A,
+	DP_TEST_LINK_RATE_RBR2      = 0x0C,	// Rate_5 (RBR2) - 3.24 Gbps/Lane
+	DP_TEST_LINK_RATE_RATE_6    = 0x10,	// Rate_6        - 4.32 Gbps/Lane
 	DP_TEST_LINK_RATE_HBR2		= 0x14,
+	DP_TEST_LINK_RATE_RATE_8    = 0x19,	// Rate_8        - 6.75 Gbps/Lane
 	DP_TEST_LINK_RATE_HBR3		= 0x1E,
 	DP_TEST_LINK_RATE_UHBR10	= 0x01,
 	DP_TEST_LINK_RATE_UHBR20	= 0x02,