genirq: Rename setup_affinity() to irq_setup_affinity()

Rename it with a proper irq_ prefix and make it available for other files
in the core code. Preparatory patch for moving the irq affinity setup
around.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Link: http://lkml.kernel.org/r/20170619235444.928501004@linutronix.de

kernel/irq/internals.h

@@ -116,6 +116,12 @@ extern void irq_set_thread_affinity(struct irq_desc *desc);
 extern int irq_do_set_affinity(struct irq_data *data,
 			       const struct cpumask *dest, bool force);
 
+#ifdef CONFIG_SMP
+extern int irq_setup_affinity(struct irq_desc *desc);
+#else
+static inline int irq_setup_affinity(struct irq_desc *desc) { return 0; }
+#endif
+
 /* Inline functions for support of irq chips on slow busses */
 static inline void chip_bus_lock(struct irq_desc *desc)
 {