arm: realm: add hvc and RSI_HOST_CALL tests

Test that a HVC instruction in a Realm is turned into an undefined exception.

Test that RSI_HOST_CALL passes through to the Hypervisor.

Signed-off-by: Gareth Stockwell <gareth.stockwell@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Joey Gouly <joey.gouly@arm.com>