dt-bindings: i2c: add entry for hisilicon,ascend910-i2c

Add the new compatible for HiSilicon i2c.

Signed-off-by: Weilong Chen <chenweilong@huawei.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>