gpio: xlp: GPIO controller for Netlogic XLP SoCs

Add GPIO controller driver for Netlogic XLP MIPS64 SOCs.

This driver is instantiated by device tree and supports interrupts
for GPIOs.

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