perf_counter, x86: remove vendor check in fixed_mode_idx()

The function fixed_mode_idx() is used generically. Now it checks the
num_counters_fixed value instead of the vendor to decide if fixed
counters are present.

[ Impact: generalize code ]

Signed-off-by: Robert Richter <robert.richter@amd.com>
Cc: Paul Mackerras <paulus@samba.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1241002046-8832-28-git-send-email-robert.richter@amd.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>