scsi: flip the default on use_clustering

driver inclusion
category: bugfix
bugzilla: NA
CVE: NA

Most SCSI drivers want to enable "clustering", that is merging of
segments so that they might span more than a single page.  Remove the
ENABLE_CLUSTERING define, and require drivers to explicitly set
DISABLE_CLUSTERING to disable this feature.

Signed-off-by: Wang Chao <wangchao342@hisilicon.com>
Reviewed-by: Zhu Xiongxiong <zhuxiongxiong@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>