drm/amd/display: DP link validation bug for YUV422

remove limit YUV422 color depth to 24bits which is
workaround for old ASIC

Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>