perf tools: Fix perf_event.h header usage

This patch fixes the usage of the perf_event.h header file
between command modules and the supporting code in util.

It is necessary to ensure that ALL files use the SAME
perf_event.h header from the kernel source tree.

There were a couple of #include <linux/perf_event.h> mixed
with #include "../../perf_event.h".

This caused issues on some distros because of mismatch
in the layout of struct perf_event_attr. That eventually
led perf stat to segfault.

Cc: David S. Miller <davem@davemloft.net>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Stephane Eranian <eranian@gmail.com>
LKML-Reference: <4d233cf0.2308e30a.7b00.ffffc187@mx.google.com>
Signed-off-by: Stephane Eranian <eranian@google.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>