powerpc/8xx: Adding support of IRQ in MPC8xx GPIO

This patch allows the use of IRQ to notify the change of GPIO status
on MPC8xx CPM IO ports. This then allows to associate IRQs to GPIOs
in the Device Tree.

Ex:
	CPM1_PIO_C: gpio-controller@960 {
		#gpio-cells = <2>;
		compatible = "fsl,cpm1-pario-bank-c";
		reg = <0x960 0x10>;
		fsl,cpm1-gpio-irq-mask = <0x0fff>;
		interrupts = <1 2 6 9 10 11 14 15 23 24 26 31>;
		interrupt-parent = <&CPM_PIC>;
		gpio-controller;
	};

The property 'fsl,cpm1-gpio-irq-mask' defines which of the 16 GPIOs
have the associated interrupts defined in the 'interrupts' property.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <oss@buserror.net>