pinctrl: sirf: switch driver to use gpiolib irqchip helpers

This switches the SiRF pinctrl driver over to using the gpiolib
irqchip helpers simplifying some of the code.

Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>