erofs-utils: switch other source files into MIT license

Let's switch other source files to MIT license since we're absolutely
not working on secret rocket science, so licenses should not be
a bottleneck to innovation in the Cloud Native and AI era.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Hongbo Li <lihongbo22@huawei.com>
Reviewed-by: Chunhai Guo <guochunhai@vivo.com>
Reviewed-by: Yifan Zhao <zhaoyifan28@huawei.com>
Link: https://lore.kernel.org/r/20260402060907.2268323-2-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>