ARM: pxa: rename gpio_to_irq and irq_to_gpio

Avoid to define gpio_to_irq() and irq_to_gpio() for potential name
confliction since multiple architecture will be built together.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>

Conflicts:
	drivers/gpio/gpio-pxa.c