powerpc/perf_counter: Enable alternate PR/HV bits for POWER7

POWER7 has the same PR/HV bit layout as POWER6, so set the flag.

Signed-off-by: Anton Blanchard <anton@samba.org>
Acked-by: Paul Mackerras <paulus@samba.org>
Cc: a.p.zijlstra@chello.nl
Cc: benh@kernel.crashing.org
LKML-Reference: <20090701030701.GI3563@kryten>
Signed-off-by: Ingo Molnar <mingo@elte.hu>