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
ls1028a GPIO node.

Signed-off-by: Song Hui <hui.song_1@nxp.com>
Link: https://lore.kernel.org/r/20190807021254.49092-1-hui.song_1@nxp.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>