arm64: dts: hisilicon: hi3670: Add MMC controller support

Add MMC controller support for HiSilicon HI3670 SoC reusing the HI3660
Designware MMC driver. There are 2 DWMMC controllers present in this SoC:

1. DWMMC1 is used for SD card (SD)
2. DWMMC2 is used for WiFi (SDIO)

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