efi: Add a script to build an image for testing on UEFI

It is quite complicated to run U-Boot on QEMU since we have four
different builds and they must use different versions of qemu and the
UEFI binaries.

Add a script to help. It requires U-Boot itself to be built. Once that
is done you can use this script to build an image for use with qemu and
optionally run it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index 9d8cba9..fa7fe90 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -710,6 +710,7 @@
 S:	Maintained
 W:	https://u-boot.readthedocs.io/en/latest/develop/uefi/u-boot_on_efi.html
 F:	lib/efi/efi_app.c
+F:	scripts/build-efi.sh
 
 EFI PAYLOAD
 M:	Heinrich Schuchardt <xypron.glpk@gmx.de>