ARM: mxs: Add support for the Armadeus Systems APF28Dev docking board

The APF28Dev is a docking board for an APF28 SOM

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