drm/i915/gvt: Use real time to do timer check

drm/i915/gvt: Use real time to do timer check

intel_gvt_schedule check timer through a counter and is supposed
to wake up to increase the counter every ms.
In a system with heavy workload, gvt_service_thread can not get
a chance to run right after wake up and will be delayed several
milliseconds. As a result, one hundred counter interval means
several hundred milliseconds in real time.

This patch use real time instead of counter to do timer check.

v2: remove static variable. (Zhenyu)
v3: correct expire_time update. (Zhenyu)

Signed-off-by: Zhipeng Gong <zhipeng.gong@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Min He <min.he@intel.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>