gpio: mpc8xxx: Add ls1028a device specify function.

There is a device specify register(named GPIO_IBE)
on ls1028a need to enable in initial stage.

Signed-off-by: Song Hui <hui.song_1@nxp.com>
Link: https://lore.kernel.org/r/20190718094902.15562-2-hui.song_1@nxp.com


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