units: unconditionally pull in remote-cryptsetup.target in the initramfs

[zjs: Replaces #17149.

I took half of the patch in
https://github.com/systemd/systemd/pull/17149#issuecomment-698399194,
hence I'm keeping Jonathan's authorship.

The original reasoning for 6c5496c492 was that we
enable remote-cryptsetup.target via presets, and since presets are not used for
the initrd, we need a different target. But since parts of the unit and target
tree are shared between the initramfs and the main system, we can't just create
a separate target for the initramfs. All the targets that depend on this one
would need to be split also. That condition is true for initrd-fs.target, but
not for sysinit.target.

So let's instead just uncoditionally pull in remote-cryptsetup.target in the
initramfs. It should normally be empty, so there should be no impact on boots
that don't have units in the target.

Jonathan's patch used initrd-root-fs.target, this version instead uses
initrd-root-device.target. initrd-root-device.target is ordered before
sysroot.mount, which means that the decrypted devices will be available earlier
too.]

units/meson.build

@@ -60,7 +60,8 @@ units = [
         ['proc-sys-fs-binfmt_misc.mount',       'ENABLE_BINFMT'],
         ['reboot.target',                       '',
          'ctrl-alt-del.target' + (with_runlevels ? ' runlevel6.target' : '')],
-        ['remote-cryptsetup.target',            'HAVE_LIBCRYPTSETUP'],
+        ['remote-cryptsetup.target',            'HAVE_LIBCRYPTSETUP',
+         'initrd-root-device.target.wants/'],
         ['remote-fs-pre.target',                ''],
         ['remote-fs.target',                    ''],
         ['rescue.target',                       '',