dt-bindings: mmc: Convert Cadence SD/SDIO/eMMC controller to json-schema

Convert the Cadence SD/SDIO/eMMC host controller IP (a.k.a. SD4HC)
binding to DT schema format.

Socionext UniPhier ARM 64-bit SoCs are integrated with this IP.

Cc: Piotr Sroka <piotrs@cadence.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Rob Herring <robh@kernel.org>