sandbox: add FAT to the list of usable env drivers

Add the FAT environment driver to the priority list.

When testing the UEFI sub-system the EFI system partition is formatted with
FAT so it is reasonable to store the environment there.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
1 file changed