[POWERPC] Split virq setup logic out into irq_setup_virq()

A future patch will need the logic at the end of irq_create_mapping()
which setups a virq and installs it in the irq_map. So split it out
into a new function irq_setup_virq().
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/irq.c

@@ -596,6 +596,25 @@ static void irq_radix_rdunlock(unsigned long flags)
 	local_irq_restore(flags);
 }
 
+static int irq_setup_virq(struct irq_host *host, unsigned int virq,
+			    irq_hw_number_t hwirq)
+{
+	/* Clear IRQ_NOREQUEST flag */
+	get_irq_desc(virq)->status &= ~IRQ_NOREQUEST;
+
+	/* map it */
+	smp_wmb();
+	irq_map[virq].hwirq = hwirq;
+	smp_mb();
+
+	if (host->ops->map(host, virq, hwirq)) {
+		pr_debug("irq: -> mapping failed, freeing\n");
+		irq_free_virt(virq, 1);
+		return -1;
+	}
+
+	return 0;
+}
 
 unsigned int irq_create_mapping(struct irq_host *host,
 				irq_hw_number_t hwirq)
@@ -644,18 +663,9 @@ unsigned int irq_create_mapping(struct irq_host *host,
 	}
 	pr_debug("irq: -> obtained virq %d\n", virq);
 
-	/* Clear IRQ_NOREQUEST flag */
-	get_irq_desc(virq)->status &= ~IRQ_NOREQUEST;
-
-	/* map it */
-	smp_wmb();
-	irq_map[virq].hwirq = hwirq;
-	smp_mb();
-	if (host->ops->map(host, virq, hwirq)) {
-		pr_debug("irq: -> mapping failed, freeing\n");
-		irq_free_virt(virq, 1);
+	if (irq_setup_virq(host, virq, hwirq))
 		return NO_IRQ;
-	}
+
 	return virq;
 }
 EXPORT_SYMBOL_GPL(irq_create_mapping);