efi_loader: load distro dtb in bootmgr

If no device-tree is specified, try to load a device-tree from the boot
device use the $fdtfile concatenated to either of the paths '/dtb/', '/',
'/dtb/current/'.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/include/efi_loader.h b/include/efi_loader.h
index ab7bed2..6c993e1 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -1205,4 +1205,6 @@
 
 int efi_get_distro_fdt_name(char *fname, int size, int seq);
 
+void efi_load_distro_fdt(void **fdt, efi_uintn_t *fdt_size);
+
 #endif /* _EFI_LOADER_H */