[MIPS] IP27: Convert to clock_event_device.

This separates the tick timer stuff from the generic MIPS time.c.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/sgi-ip27/ip27-irq.c b/arch/mips/sgi-ip27/ip27-irq.c
index 856649c..1bb692a 100644
--- a/arch/mips/sgi-ip27/ip27-irq.c
+++ b/arch/mips/sgi-ip27/ip27-irq.c
@@ -374,14 +374,13 @@
 	return irq;
 }
 
-extern void ip27_rt_timer_interrupt(void);
-
 asmlinkage void plat_irq_dispatch(void)
 {
 	unsigned long pending = read_c0_cause() & read_c0_status();
+	extern unsigned int rt_timer_irq;
 
 	if (pending & CAUSEF_IP4)
-		ip27_rt_timer_interrupt();
+		do_IRQ(rt_timer_irq);
 	else if (pending & CAUSEF_IP2)	/* PI_INT_PEND_0 or CC_PEND_{A|B} */
 		ip27_do_irq_mask0();
 	else if (pending & CAUSEF_IP3)	/* PI_INT_PEND_1 */