install: allow to use last block for embedding (MR 2069)

Devices such as ODROIDs have binaries use which every single block for
embedding. Do not raise an error when binaries are touching, but not
overlapping, each other when embedding these binaries during installation.

Add a test for this scenario, which fails when reverting the change.

Co-Authored-By: Oliver Smith <ollieparanoid@postmarketos.org>