sparseirq: fix Alpha build failure

Impact: build fix on Alpha

-tip testing found this build failure on the Alpha defconfig:

/home/mingo/tip/fs/proc/stat.c: In function 'show_stat':
/home/mingo/tip/fs/proc/stat.c:48: error: implicit declaration of function 'for_each_irq_desc'
/home/mingo/tip/fs/proc/stat.c:48: error: expected ';' before '{' token

can not use irq_desc() in stat.c on older architectures.

Signed-off-by: Yinghai Lu <yinghai@kernel.orgg>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/irqnr.h b/include/linux/irqnr.h
index 7a299e98..13754f8 100644
--- a/include/linux/irqnr.h
+++ b/include/linux/irqnr.h
@@ -8,9 +8,22 @@
 # define for_each_irq_desc(irq, desc)		\
 	for (irq = 0; irq < nr_irqs; irq++)
 
-static inline early_sparse_irq_init(void)
-{
-}
+# define for_each_irq_desc_reverse(irq, desc)                          \
+	for (irq = nr_irqs - 1; irq >= 0; irq--)
+#else
+#ifndef CONFIG_SPARSE_IRQ
+
+struct irq_desc;
+extern int nr_irqs;
+# define for_each_irq_desc(irq, desc)		\
+	for (irq = 0, desc = irq_desc; irq < nr_irqs; irq++, desc++)
+# define for_each_irq_desc_reverse(irq, desc)                          \
+	for (irq = nr_irqs - 1, desc = irq_desc + (nr_irqs - 1);        \
+	    irq >= 0; irq--, desc--)
 #endif
+#endif
+
+#define for_each_irq_nr(irq)                   \
+       for (irq = 0; irq < nr_irqs; irq++)
 
 #endif