Add Mitac MioA701 board initial support.
The support provides basic boot and :
 - a console over USB (serial gadget).
 - the SD card support
 - the MTD docg3 support
 - the LCD support

Add a check in the default environment for a barebox.env
file on the first partition (FAT). If the file exists,
source it instead of the normal boot procedure.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>