f2fs: introduce time and interval facility

This patch adds time and interval arrays to store some timing variables.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 5dbafd5..3842af9 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -1139,7 +1139,7 @@
 			"checkpoint: version = %llx", ckpt_ver);
 
 	/* do checkpoint periodically */
-	sbi->cp_expires = round_jiffies_up(jiffies + HZ * sbi->cp_interval);
+	f2fs_update_time(sbi, CP_TIME);
 	trace_f2fs_write_checkpoint(sbi->sb, cpc->reason, "finish checkpoint");
 out:
 	mutex_unlock(&sbi->cp_mutex);