OvmfPkg/QemuBootOrderLib: add StoreQemuBootOrder()

The function reads the boot order from qemu fw_cfg, translates it into
device paths and stores them in 'QemuBootOrderNNNN' variables.  In case
there is no boot ordering configured the function will do nothing.

Use case: Allow applications loaded via 'qemu -kernel bootloader.efi'
obey the boot order.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

OvmfPkg/Include/Library/QemuBootOrderLib.h

@@ -47,6 +47,20 @@ ConnectDevicesFromQemu (
   VOID
   );
 
+/**
+  Write qemu boot order to uefi variables.
+
+  Attempt to retrieve the "bootorder" fw_cfg file from QEMU. Translate
+  the OpenFirmware device paths therein to UEFI device path fragments.
+
+  On Success store the device path in QemuBootOrderNNNN variables.
+**/
+VOID
+EFIAPI
+StoreQemuBootOrder (
+  VOID
+  );
+
 /**
 
   Set the boot order based on configuration retrieved from QEMU.