tracing: Export trace_profile_buf symbols

ERROR: "trace_profile_buf_nmi" [fs/jbd2/jbd2.ko] undefined!
ERROR: "trace_profile_buf" [fs/jbd2/jbd2.ko] undefined!
ERROR: "trace_profile_buf_nmi" [fs/ext4/ext4.ko] undefined!
ERROR: "trace_profile_buf" [fs/ext4/ext4.ko] undefined!
ERROR: "trace_profile_buf_nmi" [arch/x86/kvm/kvm.ko] undefined!
ERROR: "trace_profile_buf" [arch/x86/kvm/kvm.ko] undefined!

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <1253442878.7542.3.camel@laptop>
[ fixed whitespace noise and checkpatch complaint ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>