gpio: pca953x: add support for TCA9538

The TCA9538 is an 8 bit version of the already supported TCA9539.
This chip also has interrupt support.

Signed-off-by: Liam Beguin <liambeguin@gmail.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>