erofs-utils: mkfs: enable block map chunk format

Use 4-byte block map format by default unless a blob device is
given or chunk index format is forcely specified.

Link: https://lore.kernel.org/r/20211117015757.3323-1-xiang@kernel.org
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
5 files changed