kselftest/arm64: mte: user_mem: add test type enum

The test is currently hardcoded to use the `read` syscall, this commit adds
a test_type enum to support expanding the test coverage to other syscalls.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Tested-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220209152240.52788-5-joey.gouly@arm.com


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