erofs-utils: tests: implement MD5 checksum for fssum

This patch adds MD5 checksum initialization and some other related
operations, providing support for subsequent implementation of checksum
calculation for erofs image file.

Signed-off-by: Jiawei Wang <kyr1ewang@qq.com>
Signed-off-by: Gao Xiang <xiang@kernel.org>
2 files changed