alpha: Fix HW performance counters to be stopped properly

Also fix a few compile errors due to undefined and duplicated
variables.

Signed-off-by: Michael Cree <mcree@orcon.net.nz>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1284269844-23251-1-git-send-email-mcree@orcon.net.nz>
Signed-off-by: Ingo Molnar <mingo@elte.hu>