Add Armadeus systems APF28 SOM basic support.

Buildroot toolchain, UBIFS rootfs, Linux kernel (board is mainlined
since 3.8).

Signed-off-by: Julien Boibessot <julien.boibessot@armadeus.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>