drm/amd/display: Add DPIA Link Encoder Assignment Fix

For DPIA we should have preferred DIG assignment based on DPIA selected
as per the ASIC design.

Reviewed-by: George Shen <george.shen@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Mustapha Ghaddar <mghaddar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org