bootmeth: use efi_loader interfaces instead of bootefi command

Now that efi_loader subsystem provides interfaces that are equivalent
with bootefi command, we can replace command invocations with APIs.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
diff --git a/boot/bootmeth_efi_mgr.c b/boot/bootmeth_efi_mgr.c
index 6428c09..ed29d7e 100644
--- a/boot/bootmeth_efi_mgr.c
+++ b/boot/bootmeth_efi_mgr.c
@@ -87,7 +87,7 @@
 	int ret;
 
 	/* Booting is handled by the 'bootefi bootmgr' command */
-	ret = run_command("bootefi bootmgr", 0);
+	ret = efi_bootmgr_run(EFI_FDT_USE_INTERNAL);
 
 	return 0;
 }