gpio: pca953x: Add support for the On Semi pca9655

The On Semi pca9655 is a 16 bit variant of the On Semi pca9654 GPIO
expander, with 16 GPIOs and interrupt functionality.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
[Bartosz: fixed indentation as noted by Andy]
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>