perf config: Use new perf_config_set__init() to initialize config set

Instead of perf_config(), this function initializes config set by
reading various files: user config ~/.perfconfig and system config
$(sysconfdir)/perfconfig).

If there are the same config variable in both user and system config
files, user config has higher priority than system config.

Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1465291577-20973-3-git-send-email-treeze.taeung@gmail.com


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