drm/amd/display: Do not disable pipe split if mode is not supported

[WHY]
If mode is not supported, pipe split should not be disabled.
This may cause more modes to fail.

[HOW]
Check for mode support before disabling pipe split.

This commit was previously reverted as it was thought to
have problems, but those issues have been resolved.
Signed-off-by: Sung Lee <sung.lee@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_resource.c

@@ -2623,19 +2623,24 @@ int dcn20_validate_apply_pipe_split_flags(
 
 	/* Avoid split loop looks for lowest voltage level that allows most unsplit pipes possible */
 	if (avoid_split) {
+		int max_mpc_comb = context->bw_ctx.dml.vba.maxMpcComb;
+
 		for (i = 0, pipe_idx = 0; i < dc->res_pool->pipe_count; i++) {
 			if (!context->res_ctx.pipe_ctx[i].stream)
 				continue;
 
 			for (vlevel_split = vlevel; vlevel <= context->bw_ctx.dml.soc.num_states; vlevel++)
-				if (context->bw_ctx.dml.vba.NoOfDPP[vlevel][0][pipe_idx] == 1)
+				if (context->bw_ctx.dml.vba.NoOfDPP[vlevel][0][pipe_idx] == 1 &&
+						context->bw_ctx.dml.vba.ModeSupport[vlevel][0])
 					break;
 			/* Impossible to not split this pipe */
 			if (vlevel > context->bw_ctx.dml.soc.num_states)
 				vlevel = vlevel_split;
+			else
+				max_mpc_comb = 0;
 			pipe_idx++;
 		}
-		context->bw_ctx.dml.vba.maxMpcComb = 0;
+		context->bw_ctx.dml.vba.maxMpcComb = max_mpc_comb;
 	}
 
 	/* Split loop sets which pipe should be split based on dml outputs and dc flags */