f2fs: add REQ_TIME time update for some user behaviors

some user behaviors requested filesystem operations, which
will cause filesystem not idle.
Meanwhile adjust some f2fs_update_time(REQ_TIME) positions.

Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>