ARM: imx: pass gpio than irq number into mxc_expio_init

Change mxc_expio_init interface a little bit to have gpio than irq
number passed in.  With the change, gpio_to_irq can be called inside
mxc_expio_init to get irq number, so that MXC_IRQ_TO_GPIO can be
removed.

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