block: Record writing and mounting regardless of whether bdev_allow_write_mounted is set

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


CVE: NA

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Introduce bd_mounted to record the state of mount.
The count of bd_writers and bd_mounted can have other uses and they
doesn't block writes when bdev_allow_write_mounted is not set, so remove
the restriction for recording them.

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