drm/amdgpu: add number of hardware submissions to amdgpu_fence_driver_init_ring

Make this a parameter instead of using the global variable directly.

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>