OvmfPkg/Microvm: PlatformPei/MemDetect tweaks

Skip host bridge setup on microvm.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3599
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Jiewen Yao <Jiewen.yao@intel.com>

OvmfPkg/PlatformPei/MemDetect.c

@@ -135,6 +135,10 @@ QemuUc32BaseInitialization (
   UINT32 LowerMemorySize;
   UINT32 Uc32Size;
 
+  if (mHostBridgeDevId == 0xffff /* microvm */) {
+    return;
+  }
+
   if (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) {
     //
     // On q35, the 32-bit area that we'll mark as UC, through variable MTRRs,