dt-bindings: mmc: dw_mmc-k3: add document of hi3660 mmc

Add bindings for hi3660 mmc support
Signed-off-by: NLi Wei <liwei213@huawei.com>
Signed-off-by: NGuodong Xu <guodong.xu@linaro.org>
Signed-off-by: NWei Xu <xuwei5@hisilicon.com>

Documentation/devicetree/bindings/mmc/k3-dw-mshc.txt

@@ -12,6 +12,7 @@ extensions to the Synopsys Designware Mobile Storage Host Controller.
 Required Properties:
 
 * compatible: should be one of the following.
+  - "hisilicon,hi3660-dw-mshc": for controllers with hi3660 specific extensions.
   - "hisilicon,hi4511-dw-mshc": for controllers with hi4511 specific extensions.
   - "hisilicon,hi6220-dw-mshc": for controllers with hi6220 specific extensions.