gpio: pca953x: add more register definitions for pcal953x

PCAL chips ("L" seems to stand for "latched") have additional
registers starting at address 0x40 to control the latches,
interrupt mask, pull-up and pull down etc.

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>