scripts: modules: Mark the build as tainted if blobs present

Whenever binary blobs are present in the filesystem (i.e. fetched,
regardless of whether they are up-to-date or not) we consider the Zephyr
build as tainted. In order to ensure that it is marked as so, add a
Kconfig `select` statement whenever this is the case.

Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>