gpio/lpc32xx: Add device tree support

This patch adds device tree support for gpio-lpc32xx.c.

To register the various GPIO banks as (struct) gpio_chips via the same DT
gpio-controller, we utilize the adjusted of_xlate API to manipulate the
actually used struct gpio_chip.

Signed-off-by: Roland Stigge <stigge@antcom.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>