f2fs: introduce F2FS_QUOTA_DEFAULT_FL for cleanup

This patch adds F2FS_QUOTA_DEFAULT_FL to include two default flags:
F2FS_NOATIME_FL and F2FS_IMMUTABLE_FL, and use it to clean up codes.

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>