board: add support for VIA VAB-820/AMOS-820

The VIA VAB-820 board (and the AMOS-820 system built around it) is
based on Freescale i.MX6 for embedded and industrial computing.

Signed-off-by: Gergely Imreh <imrehg@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>