powerpc/mpc8xxx_gpio: simplify searching for 'fsl, qoriq-gpio' compatiable

Commit da3ed89e added
'fsl,qoriq-gpio' compatiable searching in the old way
using for_each_compatible_node(). But the driver have
previously been changed to use a struct of_device_id
compatible list passed to for_each_matching_node().

Add 'fsl,qoriq-gpio' compatiable to the existing
compatible list instead of adding another
for_each_compatible_node() loop.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>