irq: Kill pointless irqd_to_hw export

It makes no sense to export this trivial function.  Make it a static inline
instead.

This patch also drops virq_to_hw from arch/c6x since it is unused by that
architecture.

v2: Move irq_hw_number_t into types.h to fix ARM build failure

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>

include/linux/irq.h

@@ -263,6 +263,11 @@ static inline void irqd_clr_chained_irq_inprogress(struct irq_data *d)
 	d->state_use_accessors &= ~IRQD_IRQ_INPROGRESS;
 }
 
+static inline irq_hw_number_t irqd_to_hwirq(struct irq_data *d)
+{
+	return d->hwirq;
+}
+
 /**
  * struct irq_chip - hardware interrupt chip descriptor
  *