RFC: erofs-utils:mkfs: add unprivileged container use-case support

[Naoto Yamaguchi]

Hi Gao

I created patch for submit,  but it couldn't send using git
send-email.   Google updated security, it blocked smtp based send
email by git maybe....

Can I submit using github pull request to
https://github.com/hsiangkao/erofs-utils ?

Thanks,
Naoto Yamaguchi,
a member of Automotive Grade Linux Instrument Cluster EG.