cpuidle: lpm-levels: Correctly check if its okay to do cluster LPM

Currently cluster mode that is not supporting system level lpm can
also check if its okay to do system level lpm based on reset state.

Update to check if rpm handshake is enabled instead of reset state.

Change-Id: Ica95fd837b4e2829bfc1f822aee8f290dc021d6e
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>