sh: Add a NR_IRQS_LEGACY for external IRQ0-7.

This adds a NR_IRQS_LEGACY definition, which will be used by sparse irq.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/include/asm/irq.h

@@ -8,7 +8,8 @@
  * advised to cap this at the hard limit that they're interested in
  * through the machvec.
  */
-#define NR_IRQS 256
+#define NR_IRQS			256
+#define NR_IRQS_LEGACY		8	/* Legacy external IRQ0-7 */
 
 /*
  * Convert back and forth between INTEVT and IRQ values.