perf hists: Separate overhead and baseline columns

Currently the overhead and baseline columns are handled within single
function and the distinction is made by 'baseline hists' pointer passed
by 'struct perf_hpp::ptr'.

Since hists pointer is now part of each hist_entry, it's possible to
locate paired hists pointer directly from the passed struct hist_entry
pointer.

Also separating those 2 columns makes the code more obvious.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1349354994-17853-4-git-send-email-namhyung@kernel.org
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>