erofs-utils: complete extended inode support

There is no requirement to use extended inode (v2)
for Android, but it's obviously useful for wider
use cases.

extended inode was partially supported by obsoleted_mkfs,
complete for new erofs-utils as well.

Reviewed-by: Li Guifu <blucerlee@gmail.com>
Tested-by: Li Guifu <blucerlee@gmail.com>
Link: https://lore.kernel.org/r/20191004204630.22696-2-hsiangkao@aol.com
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
6 files changed