ima: Add macros to isolate the IMA digest list

euleros inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7YT6U



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Isolate the IMA digest list code by using macros.

changelog
v2:
	Exclude some macros for code that has already
	been merged into upstream kernel
v3:
	add patch header and fix some simple code warnings
v4:
	merge some duplicate code and add macro comments
v5:
	format the code and update the issue number
v6:
	merge duplicate code instead of isolating the entire function
Signed-off-by: Zhou Shuiqing <zhoushuiqing2@huawei.com>