drm/amd/display: Allow 4 split on 10K 420 modes

drm/amd/display: Allow 4 split on 10K 420 modes

[Why]
10K YCbCr420 does not need ODM 4:1, but it requires MPC 4 split
indicated on the flags.

[How]
Make pixel encoding and resolution size specific workaround to enable
ODM combine on YCbCr420 high resolution modes.

Signed-off-by: Chris Park <Chris.Park@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>