package/systemd: Optionally disable hwdb

package/systemd: Optionally disable hwdb

By default hwdb files are installed in /usr/lib/udev/hwdb.d
Currently they take about ~5MB. After first boot, systemd-hwdb tool
parses them and creates a binary in /etc/udev/hwdb.bin, which takes
another ~6.5MB.

In case of initramfs images, hwdb parsing is done every boot. This adds
about 2-3 seconds to boot time in case of rootfs on SDHC class 10
card (benchmarked with am335x board). NAND boot takes even longer.

Add config option to disable hwdb in systemd, for smaller images and
better boot performance.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>