drm/amdgpu: set default num_kcq to 2 under sriov

The number of kernel queues has impact on the latency under sriov
usecase. So to reduce the latency we set the default num_kcq = 2 under
sriov if not set manually.

Signed-off-by: YuBiao Wang <YuBiao.Wang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>