dt-bindings: adapt rockchip-pinctrl doc to changed bindings

Introduce the syscons for grf and pmu and deprecate the previous register
areas.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Max Schwarz <max.schwarz@online.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>