ARM: dts: rockchip: add focaltech touchscreen to rk3188-bqedison2qc

The Edison tablet uses a Focaltech touchscreen, with one speciality
that the touchscreen resolution doesn't match the display resolution
(1024x768 vs. 1280x600) which userspace will have to compensate for.

Signed-off-by: Heiko Stuebner <heiko.stuebner@bq.com>