BACKPORT: f2fs: sanity check size of nat and sit cache

Make sure number of entires doesn't exceed max journal size.

Cc: stable@vger.kernel.org
Signed-off-by: Jin Qian <jinqian@android.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

(url https://sourceforge.net/p/linux-f2fs/mailman/message/35872032)
Bug: 36819470

Change-Id: I0db498cdc996ec204f56617bba5c4ab5ac6ade14