UPSTREAM: f2fs: make BG GC more aggressive for zoned devices

Since we don't have any GC on device side for zoned devices, need more
aggressive BG GC. So, tune the parameters for that.

Change-Id: I0dbe5d9cde08046095f796c014cd00a53b8d9282
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
(cherry picked from commit 5062b5be)