Define droidcore and droidcore-unbundled in sooong-only builds

Some modules register disted files against these phonies, and
then they get disted when running `m droid dist` because they're
dependencies of droid in make. Recreate this behavior in soong-only
builds.

Bug: 388312357
Test: m --soong-only dist dists acloud and aidegen
Change-Id: I9f2300967752ce1564db44a552d41144ff40cffd