genirq: Add single IRQ reservation helper

For cases that wish to reserve a single IRQ at a given place simply
provide a wrapper in to the ranged reservation routine.

Signed-off-by: Paul Mundt <[e-mail]>
LKML-Reference: <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>

include/linux/irq.h

···
 	irq_free_descs(irq, 1);
 }
 
+static inline int irq_reserve_irq(unsigned int irq)
+{
+	return irq_reserve_irqs(irq, 1);
+}
+
 #endif /* CONFIG_GENERIC_HARDIRQS */
 
 #endif /* !CONFIG_S390 */