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.
Code is written by Ondrej Kozina.
This patch adds ability to store volume key in kernel keyring
(feature available in recent kernels) and avoid setting
key through dm-ioctl and avoiding key in table mapping.
Will be used in LUKS2.
Signed-off-by: Milan Broz <gmazyland@gmail.com>