f2fs: push some variables to debug part

Some, counters are needed only for the statistical information
while debugging.
So, those can be controlled using CONFIG_F2FS_STAT_FS,
pushing the usage for few variables under this flag.

Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/gc.c

@@ -76,7 +76,9 @@ static int gc_thread_func(void *data)
 		else
 			wait_ms = increase_sleep_time(wait_ms);
 
+#ifdef CONFIG_F2FS_STAT_FS
 		sbi->bg_gc++;
+#endif
 
 		/* if return value is not zero, no victim was selected */
 		if (f2fs_gc(sbi))