drm/i915/gvt: add full vGPU reset support

Full vGPU reset need to release all the shadow PPGGT pages to avoid
unnecessary write-protect and also should re-initialize pvinfo after
resetting vregs to keep pvinfo correct.

Signed-off-by: Ping Gao <ping.a.gao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>