OvmfPkg: detect Xen earlier

This is useful for initializing memory map.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14943 6f19259b-4bc3-4df7-8a09-765794883524

OvmfPkg/PlatformPei/Platform.c

@@ -338,14 +338,20 @@ InitializePlatform (
   )
 {
   EFI_PHYSICAL_ADDRESS  TopOfMemory;
+  UINT32 XenLeaf;
 
   DEBUG ((EFI_D_ERROR, "Platform PEIM Loaded\n"));
 
   DebugDumpCmos ();
 
+  XenLeaf = XenDetect ();
+
   TopOfMemory = MemDetect ();
 
-  InitializeXen ();
+  if (XenLeaf != 0) {
+    DEBUG ((EFI_D_INFO, "Xen was detected\n"));
+    InitializeXen (XenLeaf);
+  }
 
   ReserveEmuVariableNvStore ();