[POWERPC] Add an optional device_node pointer to the irq_host

The majority of irq_host implementations (3 out of 4) are associated
with a device_node, and need to stash it somewhere. Rather than having
it somewhere different for each host, add an optional device_node pointer
to the irq_host structure.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>

include/asm-powerpc/mpic.h

@@ -240,9 +240,6 @@ struct mpic_irq_save {
 /* The instance data of a given MPIC */
 struct mpic
 {
-	/* The device node of the interrupt controller */
-	struct device_node	*of_node;
-
 	/* The remapper for this MPIC */
 	struct irq_host		*irqhost;