package/systemd: use host-systemctl preset all to enable units

since v234 upstream recommands using systemctl preset-all to enable units.
* add a buildroot specific preset file
* use that file to disable getty@tty1
* make systemd depend on host-systemd
* remove all link-creating code that systemd does for us.

Most packages will not be affected by this change, but a few packages
were installing units without manually enabling them. Those packages
will now be automatically enabled.

The fact that those packages were not enabled is almost certainly a bug,
but it is a change of behaviour that needs to be reported

host-systemd also builds udevadm for the host. That means we no longer
need to depend on host-eudev to provide udevadm (that would conflict).

Signed-off-by: Jérémy Rosen <jeremy.rosen@smile.fr>
[yann.morin.1998@free.fr:
  - also remove the hwdb sources on fs generation
  - fix check-package errors
  - few typoes and reformatting in commit log
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

docs/manual/adding-packages-generic.txt

@@ -550,6 +550,10 @@ different steps of the build process.
   is when openrc is chosen as init system and +LIBFOO_INSTALL_INIT_OPENRC+
   has not been set, in such situation +LIBFOO_INSTALL_INIT_SYSV+ will
   be called, since openrc supports sysv init scripts.
+  When systemd is used as the init system, buildroot will automatically enable
+  all services using the +systemctl preset-all+ command in the final phase of
+  image building. You can add preset files to prevent a particular unit from
+  being automatically enabled by buildroot.
 
 * +LIBFOO_HELP_CMDS+ lists the actions to print the package help, which
   is included to the main +make help+ output. These commands can print