drm/amd/display: drop dc_validate_guaranteed

Block FP16 scaling in validate_resources codepath.

Signed-off-by: Julian Parkin <jparkin@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>