i2c: Renesas Highlander FPGA SMBus support

This adds support for the SMBus adapter found in the various FPGAs on
the Renesas Highlander platforms. Particularly the R0P7780LC0011RL and
R0P7785LC0011RL FPGAs.

Functionality is fairly restricted, in that only byte and block data
transfers are supported. Normal/fast mode and IRQ/polling are also
supported. Primarily used for various RTCs and thermal sensors.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Jean Delvare <khali@linux-fr.org>