ARM: dts: add Gateworks Ventana support

The Gateworks Ventana product family consists of several baseboard designs
based on the Freescale i.MX6 family of processors.  Each baseboard has a
different set of possible features.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>