shared: make libcryptsetup dep dlopen

Let's make libcryptsetup a dlopen() style dep for PID 1 (i.e. for
RootImage= and stuff), systemd-growfs and systemd-repart. (But leave to
be a regulra dep in systemd-cryptsetup, systemd-veritysetup and
systemd-homed since for them the libcryptsetup support is not auxiliary
but pretty much at the core of what they do.)

This should be useful for container images that want systemd in the
payload but don't care for the cryptsetup logic since dm-crypt and stuff
isn't available in containers anyway.

Fixes: #8249