alpha: Add minimal support for software performance events

In the kernel the patch enables configuration of the perf event
option, adds the perf_event_open syscall, and includes a minimal
architecture specific asm/perf_event.h header file.

Signed-off-by: Michael Cree <mcree@orcon.net.nz>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Matt Turner <mattst88@gmail.com>