perf hists: Introduce perf_hpp__setup_hists_formats()

The perf_hpp__setup_hists_formats() is to build hists-specific output
formats (and sort keys).  Currently it's only used in order to build the
output format in a hierarchy with same sort keys, but it could be used
with different sort keys in non-hierarchy mode later.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1457361308-514-2-git-send-email-namhyung@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>