package/systemd: support new v246 options

This adds switches for new options:

initrd: Installs services if systemd is used on an initramfs,
useless otherwise

kernel-install: helper scripts to update kernel with an
systemd-boot partition

analyze: tool to analyze bootup and dependencies

Signed-off-by: Norbert Lange <nolange79@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>