drm/amd/display: Don't perform rate toggle on DP2-capable FIXED_VS retimers

[WHY]
Only required if FIXED_VS retimer does not support DP2-capable.

[HOW]
Gate link rate toggle with DP 128b/132b LTTPR channel coding cap check.
Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_training_fixed_vs_pe_retimer.c

@@ -270,6 +270,7 @@ enum link_training_result dp_perform_fixed_vs_pe_training_sequence(
 
 	rate = get_dpcd_link_rate(&lt_settings->link_settings);
 
+	if (!link->dpcd_caps.lttpr_caps.main_link_channel_coding.bits.DP_128b_132b_SUPPORTED) {
 		/* Vendor specific: Toggle link rate */
 		toggle_rate = (rate == 0x6) ? 0xA : 0x6;
 
@@ -282,6 +283,7 @@ enum link_training_result dp_perform_fixed_vs_pe_training_sequence(
 		}
 
 		link->vendor_specific_lttpr_link_rate_wa = rate;
+	}
 
 	core_link_write_dpcd(link, DP_LINK_BW_SET, &rate, 1);