dt-bindings: i2c: Add S700 support for Actions Semi Soc's

Add s700 compatible string to Actions Semi SoC dt-bindings.

Signed-off-by: Parthiban Nallathambi <pn@denx.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>