arm/mxc: do not use gpio_to_irq() for static initializers

The patch defines IMX_GPIO_TO_IRQ() in mach/hardware.h and replaces
all the uses of gpio_to_irq() in static initializers with
IMX_GPIO_TO_IRQ().

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>