arm: add basic support for Rockchip RK3066a boards

This adds a generic devicetree board file and a dtsi for boards
based on the RK3066a SoCs from Rockchip.

Apart from the generic parts (gic, clocks, pinctrl) the only components
currently supported are the timers, uarts and mmc ports (all DesignWare-
based).

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Olof Johansson <olof@lixom.net>