efi_loader: add handle for UART

When loading an EFI binary via the UART we assign a UART device path to it.
But we lack a handle with that device path.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/include/efi_loader.h b/include/efi_loader.h
index f4ae84d..e390d32 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -769,6 +769,7 @@
 efi_status_t efi_dp_split_file_path(struct efi_device_path *full_path,
 				    struct efi_device_path **device_path,
 				    struct efi_device_path **file_path);
+struct efi_device_path *efi_dp_from_uart(void);
 efi_status_t efi_dp_from_name(const char *dev, const char *devnr,
 			      const char *path,
 			      struct efi_device_path **device,