pinctrl: sirf: Staticize non-exported symbol

Staticize sirfsoc_gpio_irq_map() function.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>