kselftest/arm64: Refactor parameter checking in mte_switch_mode()

kselftest/arm64: Refactor parameter checking in mte_switch_mode()

Currently we just have a big if statement with a non-specific diagnostic
checking both the mode and the tag. Since we'll need to dynamically check
for asymmetric mode support in the system and to improve debugability split
these checks out.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220419103243.24774-4-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>