hostnamed: add ACPI and Device Tree chasis detection mechanisms

Heavily "inspired" by systemd.

Testing:

1. commented CHASSIS, rebooted, run busctl (returned empty chassis).
2. installed https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/60604 and rebooted
3. run busctl again:

oneplus-fajita:~$ busctl get-property org.freedesktop.hostname1 /org/freedesktop/hostname1 org.freedesktop.
hostname1 Chassis
s "handset"
oneplus-fajita:~$ cat /etc/machine-info 
PRETTY_HOSTNAME="OnePlus 6T"
#CHASSIS="handset"
HARDWARE_VENDOR="OnePlus"
HARDWARE_MODEL="6T"

Signed-off-by: David Heidelberg david@ixit.cz