gpio: pca953x: Add support for TI TCA6418

The TI TCA6418 is a 18-channel I2C I/O expander. It is slightly
different to other models from the same family, such as TCA6416,
but has enough in common with them to make it work with just a
few tweaks, which are explained in the code's documentation.

Signed-off-by: Maria Garcia <mariagarcia7293@gmail.com>
Link: https://lore.kernel.org/r/20250703205740.45385-3-mariagarcia7293@gmail.com


Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>