block: Expand the meaning of bdev_allow_write_mounted

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8S3GW


CVE: NA

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For bdev_allow_write_mounted, there will be more subdivided scenarios and
different bits of it will be used to indicate different scenarios, so
expand it now.

Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>