mount: mount unit activated by automount unit should be only ordered against the automount unit

Both fstab-generator and pid1 are duplicating the handling of
"Before=local-fs.target" dependency for mount units.

fstab-generator is correctly skipping this dep if the mount unit is activated
by an automount unit.

However the condition used by pid1 was incorrect and missed the case when a mount
unit uses "x-systemd.automount" since in this case the mount unit should be
(only) ordered against its automount unit counterpart instead.