drm/i915/gvt: refine intel_vgpu_submission_ops as per engine ops

drm/i915/gvt: refine intel_vgpu_submission_ops as per engine ops

Using per engine ops will be more flexible, here refine sub-ops(init,
clean) as per engine operation align with reset operation. This change also
will be used in next fix patch for VM engine reset.

Cc: Fred Gao <fred.gao@intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Signed-off-by: Weinan Li <weinan.z.li@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>