powerpc/mpc8xxx_gpio: Add support for 'qoriq-gpio' controllers

Add 'fsl,qoriq-gpio' compatiable to the list we search for to bind
against for mpc8xxx_gpio.  This compatiable will be used on P1-P5xxx
QorIQ devices like P4080.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>