erofs-utils: enable incremental builds

erofs-utils: enable incremental builds

`--incremental=<data|rvsp>` are now supported for tarerofs but
only `--incremental=rvsp` works for the rebuild mode.

For example:
$ mkfs.erofs --tar=f --gzip --aufs --clean=data foo.erofs f0.tgz
$ mkfs.erofs --tar=f --gzip --aufs --incremental=data foo.erofs f1.tgz
...
$ mkfs.erofs --tar=f --gzip --aufs --incremental=data foo.erofs fn-1.tgz

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240618082414.47876-8-hsiangkao@linux.alibaba.com