cpuidle: lpm-levels: Do not predict LPM for isolated cpus

Prediction can select shallower low power mode for isolated
cpu based on historical data.

Do not predict LPMs for isolated cpus.

Change-Id: I998008ef3c578c1dccfacae8513a15dfbe397e16
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>