rootfs: Eliminate circular dependency between systemd units

rpi-reconfigure-raspi-firmware.service requires /boot/firmware to be
mounted, but mounting local filesystems requires local-fs-pre.target,
so trying to run rpi-reconfigure-raspi-firmware.service before
local-fs-pre.target results in a cyclic order dependency. systemd
breaks the cycle in an arbitrary place, and the result is unlikely to be
what we want.

Instead, delay reconfiguration of config.txt until after local
filesystems are mounted, but before sysinit.target. This breaks the cycle
(image-specs#49).

This still orders it before all non-early-boot services, because
sysinit.target is part of the DefaultDependencies; so in particular
it will finish before rpi-generate-ssh-host-keys.service starts, which
avoids the two services fighting over the dpkg lock (image-specs#45).

Resolves: image-specs#45
Resolves: image-specs#49
Signed-off-by: Simon McVittie <smcv@debian.org>

rootfs/etc/systemd/system/rpi-reconfigure-raspi-firmware.service

@@ -1,6 +1,6 @@
 [Unit]
 Description=Reconfigure raspi-firmware to regenerate config.txt matching actual hardware
-Before=local-fs-pre.target
+Before=sysinit.target
 DefaultDependencies=no
 RequiresMountsFor=/boot/firmware
 
@@ -11,4 +11,4 @@ ExecStart=/usr/sbin/dpkg-reconfigure raspi-firmware
 ExecStart=/bin/systemctl --no-reload disable %n
 
 [Install]
-RequiredBy=local-fs-pre.target
+RequiredBy=sysinit.target