efi: Add support for a hello world test program

It is useful to have a basic sanity check for EFI loader support. Add a
'bootefi hello' command which loads HelloWord.efi and runs it under U-Boot.

Signed-off-by: Simon Glass <sjg@chromium.org>
[agraf: Fix documentation, add unfulfilled kconfig dep]
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/lib/efi_loader/helloworld.c b/lib/efi_loader/helloworld.c
new file mode 100644
index 0000000..03e65ab
--- /dev/null
+++ b/lib/efi_loader/helloworld.c
@@ -0,0 +1,24 @@
+/*
+ * EFI hello world
+ *
+ * Copyright (c) 2016 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#include <common.h>
+#include <part_efi.h>
+#include <efi_api.h>
+
+efi_status_t EFIAPI efi_main(efi_handle_t handle,
+			     struct efi_system_table *systable)
+{
+	struct efi_simple_text_output_protocol *con_out = systable->con_out;
+	struct efi_boot_services *boottime = systable->boottime;
+
+	con_out->output_string(con_out, L"Hello, world!\n");
+	boottime->exit(handle, 0, 0, NULL);
+
+	return EFI_SUCCESS;
+}