drm/amdgpu: Enable mcbp under sriov by default

Enable mcbp under sriov by default. Asics with soc21 supports mcbp now
so we should set it enabled.

Signed-off-by: YuBiao Wang <YuBiao.Wang@amd.com>
Reviewed-by: Horace Chen <horace.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>