arm64: dts: hisilicon: Add Pinctrl support for HiKey970 board

Add pinctrl support based on "pinctrl-single" driver for HiKey970
development board from HiSilicon.

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>