f2fs: set default valid_thresh_ratio to 80 for zoned devices

f2fs: set default valid_thresh_ratio to 80 for zoned devices

Zoned storage devices provide marginal over-capacity space, typically
around 10%, for filesystem level storage control.

By utilizing this extra capacity, we can safely reduce the default
'valid_thresh_ratio' to 80. This action helps to significantly prevent
excessive garbage collection (GC) and the resulting power consumption,
as the filesystem becomes less aggressive about cleaning segments
that still hold a high percentage of valid data.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>