x86_64: rename irq_desc/irq_desc_alloc

change names:

          irq_desc() ==> irq_desc_alloc
	__irq_desc() ==> irq_desc

Also split a few of the uses in lowlevel x86 code.

v2: need to check if desc is null in smp_irq_move_cleanup

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/irq.h b/include/linux/irq.h
index 7b59e19..5fe1b01 100644
--- a/include/linux/irq.h
+++ b/include/linux/irq.h
@@ -191,7 +191,7 @@
 } ____cacheline_internodealigned_in_smp;
 
 extern struct irq_desc *irq_to_desc(unsigned int irq);
-extern struct irq_desc *__irq_to_desc(unsigned int irq);
+extern struct irq_desc *irq_to_desc_alloc(unsigned int irq);
 
 #ifndef CONFIG_HAVE_SPARSE_IRQ