Boot fails when a keyfile is configured for all encrypted filesystems
and no other luks devices are configured. This is because luks support is only
enabled in the initrd, when boot.initrd.luks.devices has entries. When a
fileystem has a keyfile configured though, it is setup by a custom
command, not by boot.initrd.luks.
This commit adds an internal config flag to enable luks support in the
initrd file, even if there are no luks devices configured.
2000fba561