arm64: suspend: Use cpuidle context helpers in cpu_suspend()

Use cpuidle context helpers to switch to using DAIF.IF instead
of PMR to mask interrupts, ensuring that we suspend with
interrupts being able to reach the CPU interface.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20210615111227.2454465-5-maz@kernel.org


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