ARM: pxa: move PXA_GPIO_TO_IRQ macro

Since PXA_GPIO_TO_IRQ() & MMP_GPIO_TO_IRQ() macro are depended on
arch code, move them from gpio driver to platform driver instead.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>