gpio: xlp: Convert to use gpiolib irqchip helpers

commit "325f0a (MIPS: Netlogic: Use chip_data for irq_chip methods)"
Updates "mips/netlogic/common/irq.c" to use chip_data to store interrupt
controller data pointer. Before this commit handler_data was used to
store interrupt controller data which caused errors while using
gpiochip_set_chained_irqchip.

Update XLP GPIO driver to use the gpiolib irqchip helpers.
And add missing depends on OF_GPIO in Kconfig.

Signed-off-by: Kamlakant Patel <kamlakant.patel@broadcom.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>