alpha: use set_irq_chip and push down __do_IRQ to the machine types

Also kill superfluous IRQ_DISABLED initialization, since that's the
default state of the irq_desc[i].status field.

Tested-by: Michael Cree <mcree@orcon.net.nz>
Signed-off-by: Kyle McMartin <kyle@redhat.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>
diff --git a/arch/alpha/kernel/irq.c b/arch/alpha/kernel/irq.c
index fe91298..ecfa51e 100644
--- a/arch/alpha/kernel/irq.c
+++ b/arch/alpha/kernel/irq.c
@@ -159,6 +159,11 @@
 	 * at IPL 0.
 	 */
 	local_irq_disable();
-	__do_IRQ(irq);
+	generic_handle_irq(irq);
 	irq_exit();
 }
+
+void alpha_do_IRQ(unsigned int irq, struct irq_desc *desc)
+{
+	__do_IRQ(irq);
+}