zbd/rc: Support zone capacity report by blkzone

zbd/rc: Support zone capacity report by blkzone

Linux kernel 5.9 zone descriptor interface added the new zone capacity
field defining the range of sectors usable within a zone. The blkzone
tool recently supported the zone capacity in its report zone feature.
Modify the helper function _get_blkzone_report() to support the zone
capacity field.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>