drm/i915/gvt: change resetting to resetting_eng

Use resetting_eng to identify which engine is resetting
so the rest ones' workload won't be impacted

v2:
- use ENGINE_MASK(ring_id) instead of (1 << ring_id). (Zhenyu)

Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>