f2fs: wrap all unusable_blocks_per_sec code in CONFIG_BLK_DEV_ZONED

f2fs: wrap all unusable_blocks_per_sec code in CONFIG_BLK_DEV_ZONED

The usage of unusable_blocks_per_sec is already wrapped by
CONFIG_BLK_DEV_ZONED, except for its declaration and the definitions of
CAP_BLKS_PER_SEC and CAP_SEGS_PER_SEC. This patch ensures that all code
related to unusable_blocks_per_sec is properly wrapped under the
CONFIG_BLK_DEV_ZONED option.

Signed-off-by: Yongpeng Yang <yangyongpeng@xiaomi.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>