drm/amd/display: Add minimal pipe split transition state

[WHY?] When adding/removng a plane to some configurations,
unsupported pipe programming can occur when moving to a new plane.

[HOW?]
Add a safe transistion state before programming new configuration.
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Dillon Varone <dillon.varone@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1082,7 +1082,8 @@ static void disable_dangling_plane(struct dc *dc, struct dc_state *context)
 				break;
 			}
 		}
-		if (!should_disable && pipe_split_change)
+		if (!should_disable && pipe_split_change &&
+				dc->current_state->stream_count != context->stream_count)
 			should_disable = true;
 
 		if (should_disable && old_stream) {
@@ -1690,6 +1691,7 @@ static enum dc_status dc_commit_state_no_check(struct dc *dc, struct dc_state *c
 	struct pipe_ctx *pipe;
 	int i, k, l;
 	struct dc_stream_state *dc_streams[MAX_STREAMS] = {0};
+	struct dc_state *old_state;
 
 #if defined(CONFIG_DRM_AMD_DC_DCN)
 	dc_z10_restore(dc);
@@ -1808,10 +1810,11 @@ static enum dc_status dc_commit_state_no_check(struct dc *dc, struct dc_state *c
 	for (i = 0; i < context->stream_count; i++)
 		context->streams[i]->mode_changed = false;
 
-	dc_release_state(dc->current_state);
-
+	old_state = dc->current_state;
 	dc->current_state = context;
 
+	dc_release_state(old_state);
+
 	dc_retain_state(dc->current_state);
 
 	return result;