ARM: imx: convert smp platforms to global gic_handle_irq()

Convert the SMP imx platforms to use the global gic_handle_irq()
function instead a private function.

Cc: Sascha Hauer <kernel@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>