All the boards but Mamba had wrong UBI options so far, making it impossible to
flash the built image on their respective storage medium.

Fix all of the supported boards in order to make the generated images useful.

Tested on a Mirabox, an Armada XP GP and an Openblocks AX3, and used the NAND
chip datasheet for the others.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Imre Kaloz <kaloz@openwrt.org>

SVN-Revision: 44264