drm/amdgpu: disable DRIVER_ATOMIC under SRIOV

Under SRIOV, we need disable DRIVER_ATOMIC.
Otherwise, it will trigger WARN_ON at drm_universal_plane_init.

Signed-off-by: Yintian Tao <yttao@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>