package/systemd: use systemd-hwdb for generating HWDB

udevadm has been deprecated for a while for building the HWDB,
systemd-hwdb should be used in its place.

This tool further has a switch to generate the database in
/usr which is a better place for a one-time created file
than the default /etc/udev.

The systemd-hwdb wasn't enabled yet in the host build, so do that.

Signed-off-by: Norbert Lange <nolange79@gmail.com>
[Arnout: split in two separate commits]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>