efi_loader: Add a test app

Add a simple app to use for testing. This is intended to do whatever it
needs to for testing purposes. For now it just prints a message and
exits boot services.

There was a considerable amount of discussion about whether it is OK to
call exit-boot-services and then return to U-Boot. This is not normally
done in a real application, since exit-boot-services is used to
completely disconnect from U-Boot. For now, this part is skipped.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
index 066f0ca..58d4978 100644
--- a/lib/efi_loader/Kconfig
+++ b/lib/efi_loader/Kconfig
@@ -567,6 +567,16 @@
 	  No additional space will be required in the resulting U-Boot binary
 	  when this option is enabled.
 
+config BOOTEFI_TESTAPP_COMPILE
+	bool "Compile an EFI test app for testing"
+	default y
+	help
+	  This compiles an app designed for testing. It is packed into an image
+	  by the test.py testing frame in the setup_efi_image() function.
+
+	  No additional space will be required in the resulting U-Boot binary
+	  when this option is enabled.
+
 endif
 
 source "lib/efi/Kconfig"