console: rework automatic getty on kernel console logic again

It is essential that the gettys are proper dependencies from
getty.target so that they aren't killed and immediately restarted on
runlevel changes. Hence rework the logic to implicitly add console
gettys to getty.target as dependencies.

This also adds an automatic hvc console for virtualizers.

https://bugzilla.redhat.com/show_bug.cgi?id=501720