mvebu: add a subprofile for boards based on a small NOR

Some boards only come with a small NOR on it, where UBI isn't a good solution
because of its overhead.

Add a new subprofile for such boards, that rely on the mtd split framework
instead.

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

SVN-Revision: 44263