lpm-levels: Check for need_resched just before entering PSCI

LPM driver checks for the need_resched flag to bail out in case of a
task waiting on the cpu. This currently happens at a very early state
even before the cpu and cluster prepare/config. Move this check to after
cpu and cluster prepare/config happens.

Change-Id: Id7cbd73dec1ba3a2dc822ed50f29b5af6d081511
Signed-off-by: Archana Sathyakumar <asathyak@codeaurora.org>