units: delay binfmt processing until after local-fs.target

units: delay binfmt processing until after local-fs.target

Users may use rules that refer to binaries e.g. in /opt or /usr/local,
and those directories may be separate mount points. We don't need the
binfmt rules in early boot, so let's delay the service so that we can
rely on the full local filesystem being visible.

Fixes #21178.

(cherry picked from commit 0491ab5fcd1e8a7d6c532c591dabb98a9e6ed648)