arm: realm: Add Realm attestation tests

Add tests for Attestation and measurement related RSI calls.

Signed-off-by: Mate Toth-Pal <mate.toth-pal@arm.com>
Co-developed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
[ Rewrote the test cases, keeping the core testing data/logic
  Added more test scenarios to test the ABI
]
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>