Use the new generic helper, of_cpu_node_to_id(), to map a
a phandle to the logical CPU number while parsing the
PMU irq affinity.

Cc: Will Deacon <will.deacon@arm.com>
Acked-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NSuzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: NWill Deacon <will.deacon@arm.com>