drm/amdgpu: switch to amdgpu_umc structure

create new amdgpu_umc structure to for more umc
settings in future and switch to the new structure

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Dennis Li <dennis.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>