using prebuilt kernel

Change-Id: I89a03d911e5570339b2d10a2f5f1feb0d9459d7c
remove unnecessary files

Change-Id: I83b932fe8d2dc06e9bde53a3187216dd1e985611
add prebuilt and releasetools

Change-Id: Idf22f5568b60395086dade17ebc59d2ab7db11fd