Add a testcase to check that KSM should not merge pages containing
same data with same/different MTE tag values.

This testcase has one positive tests and passes if page merging
happens according to the above rule. It also saves and restores
any modified ksm sysfs entries.
Signed-off-by: NAmit Daniel Kachhap <amit.kachhap@arm.com>
Tested-by: NCatalin Marinas <catalin.marinas@arm.com>
Acked-by: NCatalin Marinas <catalin.marinas@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20201002115630.24683-6-amit.kachhap@arm.comSigned-off-by: NWill Deacon <will@kernel.org>