The crypt_activate_by_pin_token may be used only from new
dynamicly loadable token plugins.
Also refactors code for dynamically loadable plugins so
that it does not use crypt_token_handler structure anymore.
Old structure remains used only in crypt_token_register call.
Move all keyring functions to one place and separate LUKS2 specific
code to generic handling.
Also fix possible mismatch if volume key is in keyring but it is not native
LUKS2 device (libarary cannot process such a device properly).
Reduce bloated code in low level keyring utilities code.
Move log messages higher the library code.
Also return -ENOTSUP when code was compiled out by configure
option.
