drm/i915/gvt: Add support for opregion virtualization

opregion emulated with a copy from host which leads to some display
bugs such as guest resolution adjustment failure due to host opregion
fail to claim port D support. with a fake opregion table provided
to fully emulate opregion to meet guest port requirement.

v1 - initial patch
v2 - reforamt opregion arrary with 0x02x output
v3 - opregion array removed with opregion generation on host initizaiton
v4 - rebased v3 patch from stable branch to staging branch which also has
     different struct child_device_config and addressed v3 review comments.

Signed-off-by: Xiaolin Zhang <xiaolin.zhang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/reg.h

@@ -51,6 +51,9 @@
 
 #define INTEL_GVT_OPREGION_PAGES	2
 #define INTEL_GVT_OPREGION_SIZE		(INTEL_GVT_OPREGION_PAGES * PAGE_SIZE)
+#define INTEL_GVT_OPREGION_VBT_OFFSET	0x400
+#define INTEL_GVT_OPREGION_VBT_SIZE	\
+		(INTEL_GVT_OPREGION_SIZE - INTEL_GVT_OPREGION_VBT_OFFSET)
 
 #define VGT_SPRSTRIDE(pipe)	_PIPE(pipe, _SPRA_STRIDE, _PLANE_STRIDE_2_B)