gpio: pca953x: add more register definitions for pcal6524

The pcal6524 has another set of registers to fine control
the interrupt handling.

Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>