i2c: add binding to mark a bus as SMBus

SMBus is largely compatible with I2C but there are some specifics. In
case we need them on a bus, we can now use this new binding.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
1 file changed