ARM: dts: rockchip: add rk3288-based Tinker board S

Add the actual dts for the tinker board S, which brings its own emmc
device, not therefore not requiring an sd-card to boot.

Signed-off-by: David Summers <beagleboard@davidjohnsummers.uk>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>