dt-bindings: gpio: pca953x: Add support for the NXP PCAL9554B/C

The NXP PCAL9554B is a variant of the PCA953x GPIO expander,
with 8 GPIOs, latched interrupts and some advanced configuration
options. The "C" version only differs in I2C address.

This adds the entry to the devicetree bindings.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>