tools lib fs: Adopt debugfs open strerrno method

As this is not specific to an evlist and may be used with other tools.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Don Zickus <dzickus@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-a9up9mivx1pzdf5tqrqsx62d@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

 	tools/perf/util/include/asm/hash.h

tools/lib/api/fs/debugfs.h

@@ -26,4 +26,6 @@ char *debugfs_mount(const char *mountpoint);
 
 extern char debugfs_mountpoint[];
 
+int debugfs__strerror_open(int err, char *buf, size_t size);
+
 #endif /* __API_DEBUGFS_H__ */