tile: support delivering NMIs for multicore backtrace

A new hypervisor service was added some time ago (MDE 4.2.1 or
later, or MDE 4.3 or later) that allows cores to request NMIs
to be delivered to other cores.  Use this facility to deliver
a request that causes a backtrace to be generated on each core,
and hook it into the magic SysRq functionality.

Signed-off-by: Chris Metcalf <cmetcalf@ezchip.com>

arch/tile/include/asm/irq.h

@@ -78,4 +78,9 @@ void tile_irq_activate(unsigned int irq, int tile_irq_type);
 
 void setup_irq_regs(void);
 
+#ifdef __tilegx__
+void arch_trigger_all_cpu_backtrace(bool self);
+#define arch_trigger_all_cpu_backtrace arch_trigger_all_cpu_backtrace
+#endif
+
 #endif /* _ASM_TILE_IRQ_H */