perf sched: Finish latency => atom rename and misc cleanups

- Rename 'latency' field/variable names to the better 'atom' ones

 - Reduce the number of #include lines and consolidate them

 - Gather file scope variables at the top of the file

 - Remove unused bits

No change in functionality.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>