arm64: dts: hisilicon: hikey970: Add SD and WiFi support

Add SD and WiFi support for HiKey970 board based on HI3670 SoC. Due to
the absence of the PMIC driver, fixed regulators are sourced to make the
driver working.

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