ARM: imx6: fix bogus use of irq_get_irq_data

The imx6 PM code seems to be quite creative in its use of irq_data,
using something that is very much a hardware interrupt number where
we expect a virtual one.  Yes, it worked so far, but that's only
luck, and it will definitely explode in 3.19.

Fix it by using a pair of helper functions that deal with the
actual hardware.

Tested-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Olof Johansson <olof@lixom.net>