arm64: psci: Use the MPIDR values from cpu_logical_map for cpu ids.

With the (re)introduction of cpu_logical_map in arm64 we switch to
the use of MPIDR values to identify CPUs. Update the psci code to
do that.

Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>