libchromeos: Move data_encoding from Buffet to libchromeos BUG=chromium:405714 TEST=USE=buffet ./build_packages Change-Id: I9c9d3994d1e33a05cd5c978a2697164071ce5aa0 Reviewed-on: https://chromium-review.googlesource.com/213362 Tested-by: Alex Vakulenko <avakulenko@chromium.org> Reviewed-by: Bertrand Simonnet <bsimonnet@chromium.org> Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>