Use the system wide safe value from the new API for safer
decisions

Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: kvmarm@lists.cs.columbia.edu
Signed-off-by: NSuzuki K. Poulose <suzuki.poulose@arm.com>
Acked-by: NChristoffer Dall <christoffer.dall@linaro.org>
Tested-by: NDave Martin <Dave.Martin@arm.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>