crimson/zns: manage zone size, capacity and device size

crimson/zns: manage zone size, capacity and device size

zone_size and zone_capacity are reported in 512B sectors by the
kernel. Update the superblock correctly with zone size/capacity
in bytes.
Currently we are using stat() to get the device size, but it
fails on block devices to get the size. Use BLKGETSIZE ioctl
to get the actual size of the zns device in sectors and convert
to bytes.

Signed-off-by: Aravind Ramesh <aravind.ramesh@wdc.com>