erofs-utils: lib: switch to GPL-2.0+ OR MIT dual license

Apache-2.0 is still too strict for some 3rd-party integration.

Let's switch to GPL-2.0+ OR MIT dual 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: Chunhai Guo <guochunhai@vivo.com>
Reviewed-by: Hongbo Li <lihongbo22@huawei.com>
Reviewed-by: Yifan Zhao <zhaoyifan28@huawei.com>
Link: https://lore.kernel.org/r/20260402060907.2268323-1-hsiangkao@linux.alibaba.com
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>