irqdomain: Let irq_domain_mapping display ACPI fwnode attributes

irqdomain: Let irq_domain_mapping display ACPI fwnode attributes

If the system is using ACPI, there is no of_node to display. But ACPI can
use a struct irqchip_fwid as a domain identifier, and it can be used to
display the name contained in that structure.

The output on such a system will look like this:

 pMSI      0           0           0  irqchip@00000000e1180000
 MSI      37           0           0  irqchip@00000000e1180000
 GICv2m   37           0           0  irqchip@00000000e1180000
 GICv2   448         448           0  irqchip@ffff000008003000

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Link: http://lkml.kernel.org/r/20170512115538.10767-3-marc.zyngier@arm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>