lib/sysfs: add VFS parameter to sysfs_devno_is_dm_*()

Add const struct ul_vfs_ops *vfs parameter to sysfs_devno_is_dm_hidden()
and sysfs_devno_is_dm_private() so the internal sysfs reads go through
VFS dispatch.

Wire pr->vfs in libblkid probe.c and topology/sysfs.c callers.
Non-library callers pass NULL.

Addresses: https://github.com/util-linux/util-linux/issues/4308
Signed-off-by: Karel Zak <kzak@redhat.com>