f2fs: introduce sysfs/data_io_flag to attach REQ_META/FUA

This patch introduces a way to attach REQ_META/FUA explicitly
to all the data writes given temperature.

-> attach REQ_FUA to Hot Data writes

-> attach REQ_FUA to Hot|Warm Data writes

-> attach REQ_FUA to Hot|Warm|Cold Data writes

-> attach REQ_FUA to Hot|Warm|Cold Data writes as well as
          REQ_META to Hot Data writes

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

fs/f2fs/f2fs.h

@@ -1507,6 +1507,9 @@ struct f2fs_sb_info {
 	unsigned long long write_iostat[NR_IO_TYPE];
 	bool iostat_enable;
 
+	/* to attach REQ_META|REQ_FUA flags */
+	unsigned int data_io_flag;
+
 	/* For sysfs suppport */
 	struct kobject s_kobj;
 	struct completion s_kobj_unregister;