irqchip/apple-aic: Correctly map the vgic maintenance interrupt

We currently allocate the vgic maintenance interrupt by calling into
the low-level irqdomain code. Not only this is unnecessary, but this
is also pretty wrong: we end-up skipping a bunch of irqdesc state
setup

A simple "cat /proc/interrupt" shows how wrong we are, as the
interrupt appears as "Edge" instead of "Level".

Instead, just call the standard irq_create_fwspec_mapping(), which
is the right tool for the job. Duh.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Hector Martin <marcan@marcan.st>
Link: https://lore.kernel.org/r/20230201164056.669509-1-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

drivers/irqchip/irq-apple-aic.c

@@ -1201,9 +1201,7 @@ static int __init aic_of_ic_init(struct device_node *node, struct device_node *p
 			},
 		};
 
-		vgic_info.maint_irq = irq_domain_alloc_irqs(irqc->hw_domain,
-							    1, NUMA_NO_NODE,
-							    &mi);
+		vgic_info.maint_irq = irq_create_fwspec_mapping(&mi);
 		WARN_ON(!vgic_info.maint_irq);
 	}