integrity: Add key domain tag to the search criteria

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I49KW1


CVE: NA

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Add key domain tag to the search criteria in digsig module. If the
domain tag is not set for the keys from the given keyring, it is set to
NULL and the behaviour is unchanged.

The key domain tag is added to the ima appraisal keys loaded to the
system ima keyring.

Signed-off-by: Krzysztof Struczynski <krzysztof.struczynski@huawei.com>
Reviewed-by: Zhang Tianxing <zhangtianxing3@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>