clear hi bits if not used after loading metadata from disk

clear hi bits if not used after loading metadata from disk

Functions retrieving sizes from metadata do not need to check
2TB attribute only when we can guarantee the hi bits are always
clear when the MPB_ATTR_2TB_DISK attribute is not set.

Therefore the following fields are cleared on metadata load
when not in use according to attribute:
struct imsm_disk.total_blocks_hi
struct imsm_map.pba_of_lba0_hi
struct imsm_map.blocks_per_member_hi
struct imsm_map.num_data_stripes_hi

Signed-off-by: Anna Czarnowska <anna.czarnowska@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>