tracing: Create a always_inlined __trace_buffer_lock_reserve()

As Andi Kleen pointed out in the Link below, the trace events has quite a
bit of code execution. A lot of that happens to be calling functions, where
some of them should simply be inlined. One of these functions happens to be
trace_buffer_lock_reserve() which is also a global, but it is used
throughout the file it is defined in. Create a __trace_buffer_lock_reserve()
that is always inlined that the file can benefit from.

Link: http://lkml.kernel.org/r/20161121183700.GW26852@two.firstfloor.org



Reported-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>