perf config: Mark where are config items from (user or system)

perf config: Mark where are config items from (user or system)

To write config items to a particular config file, we should know where
is each config section and item from.

Current setting functionality of perf-config use autogenerating way by
overwriting collected config items to a config file.

For example, when collecting config items from user and system config
files (i.e. ~/.perfconfig and $(sysconf)/perfconfig), perf_config_set
can contain both user and system config items.  So we should know where
each value is from to avoid merging user and system config items on user
config file.

Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Nambong Ha <over3025@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Wookje Kwon <aweee0@gmail.com>
Link: http://lkml.kernel.org/r/1478241862-31230-7-git-send-email-treeze.taeung@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>