ARM: mxs: Add support for the Armadeus Systems APF28 module

The APF28 is a small SOM built around an i.MX28 processor with 128MBytes DDR2,
256MBytes NAND Flash and an Ethernet PHY.

Signed-off-by: Julien Boibessot <julien.boibessot@armadeus.com>
Signed-off-by: Gwenhael Goavec-Merou <gwenhael.goavec-merou@armadeus.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>