pinctrl: iproc-gpio: Handle interrupts for multiple instances

When multiple instance of iproc-gpio chips are present, a fix up
message[1] is printed during the probe of second and later instances.

This issue is because driver sharing same irq_chip data structure
among multiple instances of driver.

Fix this by allocating irq_chip data structure per instance of
iproc-gpio.

[1] fix up message addressed by this patch
[  7.862208] gpio gpiochip2: (689d0000.gpio): detected irqchip that
   is shared with multiple gpiochips: please fix the driver.

Fixes: 616043d5 ("pinctrl: Rename gpio driver from cygnus to iproc")
Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Link: https://lore.kernel.org/r/1567054348-19685-3-git-send-email-srinath.mannam@broadcom.com


[Rebased on top of new irq chip set-up code]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>