perf tools: Move strlcpy() from perf to tools/lib/string.c

strlcpy() will be needed by the subcmd library.  Move it to the shared
tools/lib/string.c file which can be used by other tools.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/71e2804b973bf39ad3d3b9be10f99f2ea630be46.1450193761.git.jpoimboe@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>