drm/i915/gvt: keep oa config in shadow ctx

When populating shadow ctx from guest, we should handle oa related
registers in hw ctx, so that they will not be overlapped by guest oa
configs. This patch made it possible to capture oa data from host for
both host and guests.

Signed-off-by: Min He <min.he@intel.com>
Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>