cryptsetup: implement cryptsetup_token_open_pin for systemd-tpm2 LUKS2 token

cryptsetup: implement cryptsetup_token_open_pin for systemd-tpm2 LUKS2 token

This finishes the implementation started in commit
1f895adac287b5f1b6b854caa586093616ccc172 ("cryptsetup: add libcryptsetup TPM2
PIN support").

Note that the previous implementation took a shortcut by returning EOPNOTSUPP
instead of the correct ENOANO as per the cryptsetup documentation. This meant
that systemd-cryptsetup fell back to the non-plugin implementation in order to
ask for the PIN. Since this does not happen any more when returning ENOANO, we
need to ask for the PIN in attach_luks2_by_tpm2_via_plugin() instead like
attach_luks2_by_fido2_via_plugin() does.