units: order sysinit.target, debug-shell.service after systemd-vconsole-setup

units: order sysinit.target, debug-shell.service after systemd-vconsole-setup

Previous patch to add an implicit dependency effectively orders various getty
services after systemd-vconsole-setup.service. But I think it's cleaner to also
order the service before sysinit.target, like it was before
8125e8d38e3aa099c7dce8b0161997b8842aebdc. There might be units which don't do
use TTYVHangup= but would like to have the console fully initialized.

Also, add a manual ordering to debug-shell.service, because it has
ImplicitDependencies=no. This might delay debug-shell.service a bit, but
systemd-vconsole-setup.service has no dependencies and should be very quick, so
this should not be noticable in practice. Without the ordering, the terminal
might not have a key map loaded, making debug-shell.service hard to use.