kselftests/arm64: add PAuth tests for single threaded consistency and differently initialized keys

PAuth adds 5 different keys that can be used to sign addresses.

Add a test that verifies that the kernel initializes them to different
values and preserves them across context switches.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
Reviewed-by: Vincenzo Frascino <Vincenzo.Frascino@arm.com>
Reviewed-by: Amit Daniel Kachhap <amit.kachhap@arm.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
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/20200918104715.182310-5-boian4o1@gmail.com


Signed-off-by: Will Deacon <will@kernel.org>