drm/i915/gvt: vGPU PCI configuration space virtualization

This patch introduces vGPU PCI configuration space virtualization.

- Adjust the trapped GPFN(Guest Page Frame Number) window of virtual GEN
PCI BAR 0 when guest initializes PCI BAR 0 address.

- Emulate OpRegion when guest touches OpRegion.

- Pass-through a part of aperture to guest when guest initializes
aperture BAR.

Signed-off-by: Zhi Wang <zhi.a.wang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>