Add support for on-chip I2C controller used on newer UniPhier SoCs
such as PH1-Pro4, PH1-Pro5, etc.  This adapter is equipped with
8-depth TX/RX FIFOs.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>