efi_loader: export efi_system_partition_guid

The efi_system_partition_guid is needed in multiple places. Export it.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/include/efi_loader.h b/include/efi_loader.h
index 1ae47a8..156056f 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -260,6 +260,8 @@
 extern const efi_guid_t efi_global_variable_guid;
 extern const efi_guid_t efi_guid_console_control;
 extern const efi_guid_t efi_guid_device_path;
+/* GUID of the EFI system partition */
+extern const efi_guid_t efi_system_partition_guid;
 /* GUID of the EFI_DRIVER_BINDING_PROTOCOL */
 extern const efi_guid_t efi_guid_driver_binding_protocol;
 /* event group ExitBootServices() invoked */