arm64: dts: hisilicon: Rename dwmmc nodes to mmc

arm64: dts: hisilicon: Rename dwmmc nodes to mmc

The core mmc devicetree schema expects mmc controller nodes to be named
using '^mmc(@.*)?$' pattern.

The legacy Hisilicon SoC files (hi3660, hi3670, and hi6220) previously
used the 'dwmmc' prefix for their nodes. This caused warnings during
dtbs_check.

Rename the 'dwmmc' nodes to 'mmc' to comply with the standard schema and
dtbs_check warnings. The legacy phandle labels are kept intact.

Signed-off-by: Bhargav Joshi <rougueprince47@gmail.com>
Acked-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>