We already had evsel_fprintf.c, add its counterpart, so that we can
reduce evsel.h a bit more.

We needed a new perf_event_attr_fprintf.c file so as to have a separate
object to link with the python binding in tools/perf/util/python-ext-sources
and not drag symbol_conf, etc into the python binding.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-06bdmt1062d9unzgqmxwlv88@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>