[POWERPC] add virq_to_hw accessor routine

This adds an accessor routine virq_to_hw() to the
virq routines which hides the implementation details
of the virq to hwirq map.

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>

include/asm-powerpc/irq.h

@@ -135,6 +135,10 @@ struct irq_map_entry {
 
 extern struct irq_map_entry irq_map[NR_IRQS];
 
+static inline irq_hw_number_t virq_to_hw(unsigned int virq)
+{
+	return irq_map[virq].hwirq;
+}
 
 /**
  * irq_alloc_host - Allocate a new irq_host data structure