perf evsel: Allow unresolved symbol names to be printed as addresses

The fprintf_sym() and fprintf_callchain() methods now allow users to
change the existing behaviour of showing "[unknown]" as the name of
unresolved symbols to instead show "[0x123456]", i.e. its address.

The current patch doesn't change tools to use this facility, the results
from 'perf trace' and 'perf script' cotinue like:

70.109 ( 0.001 ms): qemu-system-x8/10153 poll(ufds: 0x7f2d93ffe870, nfds: 1) = 0 Timeout
                                   [unknown] (/usr/lib64/libc-2.22.so)
                                   [unknown] (/usr/lib64/libspice-server.so.1.10.0)
                                   [unknown] (/usr/lib64/libspice-server.so.1.10.0)
                                   [unknown] (/usr/lib64/libspice-server.so.1.10.0)
                                   start_thread+0xca (/usr/lib64/libpthread-2.22.so)
                                   __clone+0x6d (/usr/lib64/libc-2.22.so)

The next patch will make 'perf trace' use the new formatting.

Suggested-by: Milian Wolff <milian.wolff@kdab.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-fja1ods5vqpg42mdz09xcz3r@git.kernel.org


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