The Pyra-Handheld originally used the tca6424 but recently we have
replaced it by the pin and package compatible pcal6524. So let's
add this to the bindings and the driver.

And while we are at it, the pcal9555a does not have a compatible entry
either but is already supported by the device id table.
Signed-off-by: H. Nikolaus Schaller <hns@goldelico.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>