libmount: report kernel message from new API

libmount: report kernel message from new API

This is a very minimalistic implementation for v2.40 designed to print
error messages from the kernel. It exclusively displays errors, and
the patch does not introduce any new library interface for this
purpose. Instead, it simply replaces hardcoded messages within
libmount with kernel messages.

It's worth noting that the final implementation will necessitate
per-hook error handling in libmount and likely a new library API to
access other types of messages (warnings, notices, etc.).

Signed-off-by: Karel Zak <kzak@redhat.com>