perf hists: Introduce perf_hpp__list for period related columns

Adding perf_hpp__list list to register and contain all period related
columns the command is interested in.

This way we get rid of static array holding all possible columns and
enable commands to register their own columns.

It'll be handy for diff command in future to process and display data
for multiple files.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/n/tip-kiykge4igrcl7etmpmveto1h@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>