Add 16K boot image and dtbo image to dependency list of target files

In aosp/3236458 these two artifacts are added to target-files.zip, but
they are not listed as dependency of target-files.zip. Depending on
build order and clean spec, sometimes this leads to missing files.

Test: th
Change-Id: I70e3b3691e77112c2427d95930b0c27a8042884b