f2fs: allow address pointer number of dnode aligning to specified size

This patch expands scalability of dnode layout, it allows address pointer
number of dnode aligning to specified size (now, the size is one byte by
default), and later the number can align to compress cluster size
(1 << n bytes, n=[2,..)), it can avoid cluster acrossing two dnode, making
design of compress meta layout simple.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>