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

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>