perf trace: Clean up #includes

Removed duplicated #includes util/trace-event.h and
util/exec_cmd.h.
Grouped and sorted all the #includes.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <1281016299-23958-14-git-send-email-andrea.gelmini@gelma.net>
Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>