buildroot

configs/wandboard: Bump U-Boot and kernel versions

Bump U-Boot to 2017.09 version and kernel to 4.13.3.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>