OvmfPkg/XenBusDxe: Add support to make Xen Hypercalls.

Change in V4:
- Replace the license by the commonly used file header text.
- add file header to XenHypercall.h (license, copyright, brief desc)

Change in V3:
- adding IA32 support. (not reviewed yet)
  both XenBusDxe/Ia32/hypercall.{S,asm} file are new

Change in V2:
- file header, copyright
- Add License
- Add push/pop instruction.
- fix types
- Comment of exported functions
- Improve coding style
- Add error handling in the main init function (of the drivers)
- Comment assembly

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@16260 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/XenBusDxe/XenBusDxe.h

@@ -70,6 +70,8 @@ extern EFI_COMPONENT_NAME_PROTOCOL  gXenBusDxeComponentName;
 //
 // Other stuff
 //
+#include <IndustryStandard/Xen/xen.h>
+
 #define PCI_VENDOR_ID_XEN                0x5853
 #define PCI_DEVICE_ID_XEN_PLATFORM       0x0001
 
@@ -83,6 +85,9 @@ struct _XENBUS_DEVICE {
   EFI_DRIVER_BINDING_PROTOCOL   *This;
   EFI_HANDLE                    ControllerHandle;
   EFI_EVENT                     ExitBootEvent;
+
+  VOID                          *Hyperpage;
+  shared_info_t                 *SharedInfo;
 };
 
 #endif