kselftest/arm64: Add utilities and a test to validate mte memory

This test checks that the memory tag is present after mte allocation and
the memory is accessible with those tags. This testcase verifies all
sync, async and none mte error reporting mode. The allocated mte buffers
are verified for Allocated range (no error expected while accessing
buffer), Underflow range, and Overflow range.

Different test scenarios covered here are,
* Verify that mte memory are accessible at byte/block level.
* Force underflow and overflow to occur and check the data consistency.
* Check to/from between tagged and untagged memory.
* Check that initial allocated memory to have 0 tag.

This change also creates the necessary infrastructure to add mte test
cases. MTE kselftests can use the several utility functions provided here
to add wide variety of mte test scenarios.

GCC compiler need flag '-march=armv8.5-a+memtag' so those flags are
verified before compilation.

The mte testcases can be launched with kselftest framework as,

make TARGETS=arm64 ARM64_SUBTARGETS=mte kselftest

or compiled as,

make -C tools/testing/selftests TARGETS=arm64 ARM64_SUBTARGETS=mte CC='compiler'

Co-developed-by: Gabor Kertesz <[email protected]>
Signed-off-by: Gabor Kertesz <[email protected]>
Signed-off-by: Amit Daniel Kachhap <[email protected]>
Tested-by: Catalin Marinas <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

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