drm/amd/display: Update dummy P-state search to use DCN32 DML

[Why]
Current DCN3.2 logic for finding the dummy P-state index uses the
DCN3.0 DML validation function instead of DCN3.2 DML.

This can result in either unexpected DML VBA values, or unexpected
dummy P-state index to be used.

[How]
Update the dummy P-state logic to use DCN3.2 DML validation function.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>