gpio: pca953x: Add devices to Kconfig help

The pca953x driver supports tca6424 (24-bit) and pca9505 (40-bit)
devices. They were the only supported devices not mentioned in the
Kconfig help.

Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Acked-by: Graeme Smecher <gsmecher@threespeedlogic.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>