ppc64: move stack switching up in interrupt processing

This will make the ppc64 multiplatform irq handling more like
the generic handling.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

arch/powerpc/kernel/misc_64.S

@@ -89,12 +89,12 @@ _GLOBAL(call_do_softirq)
 	mtlr	r0
 	blr
 
-_GLOBAL(call_handle_IRQ_event)
+_GLOBAL(call_ppc_irq_dispatch_handler)
 	mflr	r0
 	std	r0,16(r1)
-	stdu	r1,THREAD_SIZE-112(r6)
-	mr	r1,r6
-	bl	.handle_IRQ_event
+	stdu	r1,THREAD_SIZE-112(r5)
+	mr	r1,r5
+	bl	.ppc_irq_dispatch_handler
 	ld	r1,0(r1)
 	ld	r0,16(r1)
 	mtlr	r0