tile: fix panic with large IRQ number

The "available_irqs" value needs to actually reflect the IRQs
available, not just start as an all-ones mask, since we only
have 32 IRQs available even on a 64-bit platform.
Signed-off-by: NChris Metcalf <cmetcalf@tilera.com>

arch/tile/kernel/irq.c

@@ -55,7 +55,8 @@ static DEFINE_PER_CPU(int, irq_depth);
 
 /* State for allocating IRQs on Gx. */
 #if CHIP_HAS_IPI()
-static unsigned long available_irqs = ~(1UL << IRQ_RESCHEDULE);
+static unsigned long available_irqs = ((1UL << NR_IRQS) - 1) &
+				      (~(1UL << IRQ_RESCHEDULE));
 static DEFINE_SPINLOCK(available_irqs_lock);
 #endif