drm/amd/display: Secondary display goes blank on Non DCN31

[Why]
Due to integration issues with branch merging,
a regression happened that prevented secondary
displays from lighting up or enabling certain features

[How]
Separated the new logic to be for DCN31 only and retained
pre DCN31 logic for all other ASICs

Reviewed-by: Wenjing Liu <[e-mail]>
Acked-by: Wayne Lin <[e-mail]>
Signed-off-by: Ahmad Othman <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/display/dc/core/dc_link.c

···
 			config.phy_idx = link_enc->transmitter - TRANSMITTER_UNIPHY_A;
 
 			// Add flag to guard new A0 DIG mapping
-			if (pipe_ctx->stream->ctx->dc->enable_c20_dtm_b0 == true) {
+			if (pipe_ctx->stream->ctx->dc->enable_c20_dtm_b0 == true &&
+					pipe_ctx->stream->link->dc->ctx->dce_version == DCN_VERSION_3_1) {
 				config.dig_be = link_enc->preferred_engine;
 				config.dio_output_type = pipe_ctx->stream->link->ep_type;
 				config.dio_output_idx = link_enc->transmitter - TRANSMITTER_UNIPHY_A;