ima: Set ML template per ima namespace

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


CVE: NA

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Set ML template based on the ima_template string. It can be defined by
the user through kcmd_for_children ima securityfs entry. Acceptable
values are the same as for the ima_template kernel boot parameter.

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