serial: max310x: implement I2C support

serial: max310x: implement I2C support

I2C implementation on this chip has a few key differences
compared to SPI, as described in previous patches.
 * extended register space access needs no extra logic
 * slave address is used to select which UART to communicate
   with

To accommodate these differences, add an I2C interface config,
set the RevID register address and implement an empty method
for setting the GlobalCommand register, since no special handling
is needed for the extended register space.

To handle the port-specific slave address, create an I2C dummy
device for each port, except the base one (UART0), which is
expected to be the one specified in firmware, and create a
regmap for each I2C device.
Add minimum and maximum slave addresses to each devtype for
sanity checking.

Also, use a separate regmap config with no write_flag_mask,
since I2C has a R/W bit in its slave address, and set the
max register to the address of the RevID register, since the
extended register space needs no extra logic.

Finally, add the I2C driver.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Cosmin Tanislav <cosmin.tanislav@analog.com>
Link: https://lore.kernel.org/r/20220605144659.4169853-5-demonsingur@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>