ARM: dts: rockchip: add BQ Edison 2 QC devicetree

The Edison 2 Quad-Core was a Tablet device released in 2013 by MundoReader
using a rk3188 soc. Add a devicetree for it.

Signed-off-by: Heiko Stuebner <heiko.stuebner@bq.com>
Reviewed-by: Rob Herring <robh@kernel.org>