drm/i915/gvt: take runtime pm when do early scan and shadow

Need to take runtime pm when do early scan/shadow of workload
for request operations.

Fixes: 7fa56bd159bc ("drm/i915/gvt: Audit and shadow workload during ELSP writing")
Cc: Ping Gao <ping.a.gao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>