units: move resolved to sysinit.target (from basic.target)

units: move resolved to sysinit.target (from basic.target)

79a67f3ca4d32c37b5e754501852a85eae908a6a pulled systemd-resolved.service
in from basic.target instead of multi-user.target, i.e. the idea is to
make it an early boot service, instead of a regular service.

However, early boot services are supposed to be in sysinit.target, not
basic.target (the latter is just one that combines the early boot
services in sysinit.target, the sockets in sockets.targt, the mounts in
local-fs.target and so on into one big target).

Also, the comit actually didn't add a synchronization point, i.e. not
Before=, so that the whole thing was racy.

Let's fix all that.

Follow-up for 79a67f3ca4d32c37b5e754501852a85eae908a6a