libblkid: add dax capability detection in topology probing

libblkid: add dax capability detection in topology probing

The dax (direct access) blockdev capability is exposed via sysfs, add it
to the list of topology values to be obtained while probing.

Expose blkid_topology_get_dax() symbol that programs can link against
for querying the capability.

Reorder the idinfos array to give precedence to the sysfs over ioctl so
that the dax probe has a chance to be executed, as there is no ioctl
interface for it.

Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>