Revert "Revert "Disable separated DTB build and remove dtbtool""

This reverts commit 408fea74fa56d2ac632c22d394da71b219546254.

Change-Id: If71160f687573e40c1298f2bcf1e825f7d6ab239
Merge "Revert "Revert "Disable separated DTB build and remove dtbtool""" into kitkat