common/rc: introduce minimal fs size check

common/rc: introduce minimal fs size check

_scratch_mkfs_sized() create a file system with specified size
limit. It can, however, too small for certain kind of devices. For
example, zoned btrfs requires at least 5 zones to make a file system.

This commit introduces MIN_FSSIZE, which specify the minimum size of the
possible file system. We can set this variable e.g. $ZONE_SIZE *
$MIN_ZONE_COUNT.

Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>