libmount: use some MS_* flags as superblock flags

libmount: use some MS_* flags as superblock flags

The old mount(2) API usually utilizes MS_* flags to set up the VFS
node. However, there are some exceptions like "sync" (MS_SYNCHRONOUS),
where the flag is used (by kernel) for the superblock instead. The new
API addresses this issue, ensuring that these options are used for
fsconfig().

This commit introduces MNT_SUPERBLOCK to identify these options in the
libmount options Linux map, and it enforces the new mount code to
utilize these options for fsconfig(FSCONFIG_SET_FLAG).

Reported-by: Abbink Esger <esger.abbink.ext@siemens.com>
Signed-off-by: Karel Zak <kzak@redhat.com>