arm: imx: Enable booting from SATA on wandboard.

Enable booting from SATA on the wandboard.

Sata support was already enabled, but distro_bootcmd is not configured
to boot from it.

Signed-off-by: Vagrant Cascadian <vagrant@debian.org>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>