cpuidle: lpm-levels: Add system_pm ops for system level LPMs

Add system_pm ops that are used by LPM driver to configure sleep
and wake votes as well as next wake up time. LPM driver uses them
during system level LPMs.

Change-Id: I72b89aeb3408b89a73d1f0c821649f4f998ab85c
Signed-off-by: Raju P.L.S.S.S.N <rplsssn@codeaurora.org>