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.