UefiPayloadPkg: Stall before connecting devices

USB devices are not being detected when booting. Pause a bit for them to
be initialized and detected by EfiBootManagerConnectAll().

UefiPayloadPkg/Library/PlatformBootManagerLib/PlatformBootManager.c

@@ -255,6 +255,9 @@ PlatformBootManagerAfterConsole (
   gST->ConOut->ClearScreen (gST->ConOut);
   BootLogoEnableLogo ();
 
+  // FIXME: USB devices are not being detected unless we wait a bit.
+  gBS->Stall (100 * 1000);
+
   EfiBootManagerConnectAll ();
   EfiBootManagerRefreshAllBootOption ();