LU-11850 lov: migrate completely to lu_tgt_descs API

LU-11850 lov: migrate completely to lu_tgt_descs API

The lov target handling was written before the generic lu_tgt
was written. Migrate to this newer API so lov can be treated
the same like lmv and lod. With the changes we have the new
lov_foreach_tgt() macro that tranverses all the registered
targets of total amount ltd->ltd_tgts_size. Also lov_tgt()
was created to extract a target by its index. Internally
a bitmap is used to tell if the tgt has been setup and
ltd->ltd_tgts_size defines the largest possible index.

Another change is that since that largest OST offset that
a striped lustre file can have is 65503 we reduce the
largest index possible for an OST since the last OSTs
could never be used.

Fixes: 1a6ef725c2 ("LU-16938 utils: setstripe overstripe multiple OST count")
Change-Id: If3f53b2a4589f93a024fa026ba377e2175282c29
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51959
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Feng Lei <flei@ddn.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>