GYP: add the Android support v17 leanback library target

Change-Id: I016eb81045553e034e9c933f57d1611660c60808
BUG=592801
Reviewed-on: https://chromium-review.googlesource.com/331350
Reviewed-by: Brett Wilson <brettw@chromium.org>
Commit-Queue: Tsung-Hung Wu <tsunghung@chromium.org>
Tested-by: Tsung-Hung Wu <tsunghung@chromium.org>
Reviewed-by: Tsung-Hung Wu <tsunghung@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>