mx5: Add registration of GPIOs for MX5 devices

Register the gpio irqs on Freescale's MX51 Babbage HW.

Signed-off-by: Dinh Nguyen <Dinh.Nguyen@freescale.com>
Signed-off-by: Amit Kucheria <amit.kucheria@canonical.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>