perf report: Allow configuring the default sort order in ~/.perfconfig

Allows changing the default sort order from "comm,dso,symbol" to some
other default, for instance "sym,dso" may be more fitting for kernel
developers.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-pm1h5puxua8nsxksd68fjm8r@git.kernel.org


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