x86: perf_counter cleanup

Use and actual unsigned long bitmap instead of casting our way around.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Jaswinder Singh Rajput <jaswinder@kernel.org>
LKML-Reference: <1236508459.22914.3645.camel@twins>
Signed-off-by: Ingo Molnar <mingo@elte.hu>