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/Makefile b/lib/efi_loader/Makefile
index 00d1896..87131ab 100644
--- a/lib/efi_loader/Makefile
+++ b/lib/efi_loader/Makefile
@@ -20,6 +20,7 @@
 ifeq ($(CONFIG_GENERATE_ACPI_TABLE),)
 apps-y += dtbdump
 endif
+apps-$(CONFIG_BOOTEFI_TESTAPP_COMPILE) += testapp
 
 obj-$(CONFIG_CMD_BOOTEFI_HELLO) += helloworld_efi.o
 obj-$(CONFIG_EFI_BOOTMGR) += efi_bootmgr.o