alpha: implement HW performance events on the EV67 and later CPUs

This implements hardware performance events for the EV67 and later CPUs
within the Linux performance events subsystem.  Only using the performance
monitoring unit in HP/Compaq's so called "Aggregrate mode" is supported.

The code has been implemented in a manner that makes extension to other
older Alpha CPUs relatively straightforward should some mug wish to
indulge themselves.

Signed-off-by: Michael Cree <mcree@orcon.net.nz>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Jay Estabrook <jay.estabrook@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>