drm/amd/display: Fixes for some MPO cases

[Why]
Alpha could be improperly applied (only affecting half the
frame) for some source pixel formats.

[How]
Change how alpha is enabled in MPC/DPP LB and change the
bottom plane blend mode in MPC.
Signed-off-by: Ilya Bakoulin <Ilya.Bakoulin@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_mpc.c

@@ -211,7 +211,7 @@ struct mpcc *mpc1_insert_plane(
 	} else {
 		new_mpcc->mpcc_bot = NULL;
 		REG_SET(MPCC_BOT_SEL[mpcc_id], 0, MPCC_BOT_SEL, 0xf);
-		REG_UPDATE(MPCC_CONTROL[mpcc_id], MPCC_MODE, MPCC_BLEND_MODE_TOP_LAYER_PASSTHROUGH);
+		REG_UPDATE(MPCC_CONTROL[mpcc_id], MPCC_MODE, MPCC_BLEND_MODE_TOP_LAYER_ONLY);
 	}
 	REG_SET(MPCC_TOP_SEL[mpcc_id], 0, MPCC_TOP_SEL, dpp_id);
 	REG_SET(MPCC_OPP_ID[mpcc_id], 0, MPCC_OPP_ID, tree->opp_id);

drivers/gpu/drm/amd/display/dc/dcn20/dcn20_hwseq.c

@@ -1863,7 +1863,7 @@ static void dcn20_update_mpcc(struct dc *dc, struct pipe_ctx *pipe_ctx)
 {
 	struct hubp *hubp = pipe_ctx->plane_res.hubp;
 	struct mpcc_blnd_cfg blnd_cfg = { {0} };
-	bool per_pixel_alpha = pipe_ctx->plane_state->per_pixel_alpha && pipe_ctx->bottom_pipe;
+	bool per_pixel_alpha = pipe_ctx->plane_state->per_pixel_alpha;
 	int mpcc_id;
 	struct mpcc *new_mpcc;
 	struct mpc *mpc = dc->res_pool->mpc;