[Why]
Newer DCN should use optc3

[How]
Declare optc3 vmin/vmax function in header.
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>