libnvdimm, btt: consolidate arena validation

libnvdimm, btt: consolidate arena validation

Orabug: 22913653

Use arena_is_valid as a common routine for checking the validity of an
info block from both discover_arenas, and nd_btt_probe.

As a result, don't check for validity of the BTT's UUID, and lbasize.
The checksum in the BTT info block guarantees self-consistency, and when
we're called from nd_btt_probe, we don't have a valid uuid or lbasize
available to check against.

Also cleanup to return a bool instead of an int.

Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
(cherry picked from commit ab45e7632717b811e0786e46ca5ad279cb731b66)
Signed-off-by: Dan Duval <dan.duval@oracle.com>