Build android_device by default in soong-only builds

This makes it so that `m --soong-only` builds all the partition
images and copies them to TARGET_OUT. (except for super.img and
userdata.img, which are still in progress)

Bug: 376727180
Test: m --soong-only, ls out/target/product/vsoc_x86_64/
Change-Id: If564869c13f2a427e1f6496199aa1b7808ab2f53