drm/amd/display: Update function to get optimal number of taps

[Why]
Diagnostics scaling test failing to set required number of vertical taps
in 4:2:0 surface case

[How]
In dpp3_get_optimal_number_of_taps() need to use LB_MEMORY_CONFIG_3 for
4:2:0 surface case. In resource_build_scaling_params() make sure to also
set plane res alpha enable based on updated surface state
Signed-off-by: Eric Bernstein <eric.bernstein@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1077,6 +1077,7 @@ bool resource_build_scaling_params(struct pipe_ctx *pipe_ctx)
 	 * on certain displays, such as the Sharp 4k
 	 */
 	pipe_ctx->plane_res.scl_data.lb_params.depth = LB_PIXEL_DEPTH_30BPP;
+	pipe_ctx->plane_res.scl_data.lb_params.alpha_en = plane_state->per_pixel_alpha;
 
 	pipe_ctx->plane_res.scl_data.recout.x += timing->h_border_left;
 	pipe_ctx->plane_res.scl_data.recout.y += timing->v_border_top;