alpha: remove obsolete hw_interrupt_type

The defines and typedefs (hw_interrupt_type, no_irq_type, irq_desc_t) have
been kept around for migration reasons.  After more than two years it's
time to remove them finally.

This patch cleans up one of the remaining users.  When all such patches
hit mainline we can remove the defines and typedefs finally.

Impact: cleanup

Convert the last remaining users to struct irq_chip and remove the
define.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Richard Henderson <rth@twiddle.net>

Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>