erofs-utils: fuse: support symlink & special inode

This patch adds symlink and special inode (e.g. block dev, char,
socket, pipe inode) support.

Link: https://lore.kernel.org/r/20201127114617.13055-3-hsiangkao@aol.com
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@aol.com>