gpiolib: Reuse device's fwnode to create IRQ domain

When IRQ domain is created for an ACPI case, the name of it becomes unknown-%d
since for now it utilizes of_node member only and doesn't consider fwnode case.
Convert IRQ domain creation code to utilize fwnode instead.

Before/After the change on Intel Galileo Gen 2 with two GPIO (IRQ) controllers:

  unknown-1	==>	\_SB.PCI0.GIP0.GPO
  unknown-2	==>	\_SB.NIO3

Due to the nature of this change we may also deduplicate the WARN():s
because in either case (DT or ACPI) the fwnode will be set correctly
and %pfw is an equivalent to what the current code prints as a prefix.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>