gpio: mpc8xxx: Add new platforms GPIO DT node description

Update the NXP GPIO node dt-binding file for QorIQ and
Layerscape platforms, and add one more example with
ls2080a GPIO node.

Signed-off-by: Liu Gang <Gang.Liu@nxp.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>