gpio: LPC32xx: Driver cleanup

Since LPC32xx is now switched over to devicetree based GPIO, the unused
lpc32xx_gpio_init() can be removed.

Further, the driver title changed since it referred to the wrong file.

Signed-off-by: Roland Stigge <stigge@antcom.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>