staging: erofs: harden inode lookup for 32-bit platforms

This patch introduces inode hash function, test and set callbacks,
and iget5_locked to find the right inode for 32-bit platforms.

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