buildroot

board/minnowboard-max: Add kernel options to support USB disks

As reported by bug #9176 the current v4.6 kernel config
(used by Minnowboard MAX and Turbot) does not support
USB disks. Since this is a pretty essential functionality,
it's desirable to have it, so let's add the required options.

Kernel config linux-v3.8.config (currently used by the first
generation Minnowboard) doesn't need this change.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>