cpuidle: lpm-levels: Fix WFI mode to work on Non-PSCI targets

Fix WFI mode to work on Non-PSCI targets. Also skip update
lpm debug events if WFI low power mode is selected.

Change-Id: If07ccddb9642ab62d2fbf936574970a1770afb8e
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>