staging: erofs: support special inode

This patch adds to support special inode, such as block dev, char,
socket, pipe inode.

Reviewed-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>