upl: Add an end-to-end test

Now that sandbox_vpl supports UPL, add a test that checks that the
payload can be loaded by SPL and the handoff information passed through
to U-Boot proper.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 215ffd0..44e9c2f 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -1720,6 +1720,7 @@
 F:	doc/usage/cmd/upl.rst
 F:	include/upl.h
 F:	test/boot/upl.c
+F:	test/py/tests/test_upl.py
 
 USB
 M:	Marek Vasut <marex@denx.de>