gpio: mpc8xxx: change the gpio interrupt flags.

Delete the interrupt IRQF_NO_THREAD flags in order to gpio interrupts
can be threaded to allow high-priority processes to preempt.

Signed-off-by: Song Hui <hui.song_1@nxp.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>