pinctrl: rockchip: add support for rk1108

This add pinctrl support for Rockchip RK1108 Soc.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>

Series-changes: 2
- add pull and drive-strength functionality

Series-changes: 3
- two minor CodingStyle fixes adviced by Heiko
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>