powerpc/85xx: Add 'fsl,pq3-gpio' compatiable for GPIO driver

Support MPC85xx platforms outside of MPC8572/MPC8536.  The
MPC8572/MPC8536 have an erratum that is worked around based on having
"fsl,mpc8572-gpio" in the compatiable list.  All other MPC85xx SoCs
don't require this workaround and thus utilize the 'fsl,pq3-gpio'
compatiable.

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