gpio/mpc8xxx: change irq handler from chained to normal

More than one gpio controllers can share one interrupt, change the
driver to request shared irq.

While this will work, it will mess up userspace accounting of the number
of interrupts per second in tools such as vmstat.  The reason is that
for every GPIO interrupt, /proc/interrupts records the count against GIC
interrupt 68 or 69, as well as the GPIO itself.  So, for every GPIO
interrupt, the total number of interrupts that the system has seen
increments by two.

Signed-off-by: Laurentiu Tudor <Laurentiu.Tudor@nxp.com>
Signed-off-by: Alex Marginean <alexandru.marginean@nxp.com>
Signed-off-by: Song Hui <hui.song_1@nxp.com>
Link: https://lore.kernel.org/r/20191011005643.41007-1-hui.song_1@nxp.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>