AZ_SAS token should be prefixed with a question mark. Add a sanity check for
this and fix the documentation.
[YOCTO #15882]
(Bitbake rev: 22011765202514600314732b97f1bb938e21f585)
Signed-off-by: Robbin Van Damme <robbinvandamme@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>