f2fs: introduce struct inode_management to wrap inner fields

Now in f2fs, we have three inode cache: ORPHAN_INO, APPEND_INO, UPDATE_INO,
and we manage fields related to inode cache separately in struct f2fs_sb_info
for each inode cache type.
This makes codes a bit messy, so that this patch intorduce a new struct
inode_management to wrap inner fields as following which make codes more neat.

/* for inner inode cache management */
struct inode_management {
	struct radix_tree_root ino_root;	/* ino entry array */
	spinlock_t ino_lock;			/* for ino entry lock */
	struct list_head ino_list;		/* inode list head */
	unsigned long ino_num;			/* number of entries */
};

struct f2fs_sb_info {
	...
	struct inode_management im[MAX_INO_ENTRY];      /* manage inode cache */
	...
}

Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 6f514fb..478ce1e 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -60,8 +60,8 @@
 		if (sbi->sb->s_bdi->dirty_exceeded)
 			return false;
 		for (i = 0; i <= UPDATE_INO; i++)
-			mem_size += (sbi->ino_num[i] * sizeof(struct ino_entry))
-							>> PAGE_CACHE_SHIFT;
+			mem_size += (sbi->im[i].ino_num *
+				sizeof(struct ino_entry)) >> PAGE_CACHE_SHIFT;
 		res = mem_size < ((avail_ram * nm_i->ram_thresh / 100) >> 1);
 	}
 	return res;