OvmfPkg: PlatformBdsLib: signal gRootBridgesConnectedEventGroupGuid

The explanation is in the patch titled

  OvmfPkg: introduce gRootBridgesConnectedEventGroupGuid

At this point, this signal doesn't do anything yet.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

OvmfPkg/Library/PlatformBdsLib/BdsPlatform.c

@@ -13,6 +13,7 @@
 **/
 
 #include "BdsPlatform.h"
+#include <Guid/RootBridgesConnectedEventGroup.h>
 #include <Library/QemuBootOrderLib.h>
 
 
@@ -1244,6 +1245,11 @@ Returns:
   VisitAllInstancesOfProtocol (&gEfiPciRootBridgeIoProtocolGuid,
     ConnectRootBridge, NULL);
 
+  //
+  // Signal the ACPI platform driver that it can download QEMU ACPI tables.
+  //
+  EfiEventGroupSignal (&gRootBridgesConnectedEventGroupGuid);
+
   //
   // We can't signal End-of-Dxe earlier than this. Namely, End-of-Dxe triggers
   // the preparation of S3 system information. That logic has a hard dependency