msm: pm-8x60: Do not default to WFI when not enabled

Return MSM_PM_SLEEP_MODE_NOT_SELECTED in msm_pm_idle_prepare as the
default mode instead of WFI. Skip enter low power mode when this
mode is selected.

Change-Id: Id4a07ba1353b358726c81ed441e0327a9154de8a
Signed-off-by: Priyanka Mathur <pmathur@codeaurora.org>
msm: pm-8x60: Use ktime_get for suspend stats

During suspend, the sched clock is stopped and the suspends ops
cannot rely on sched clock to report time spent in suspend. Use ktime
interface to determine the time spent in suspend.

Change-Id: Id244cd8d470c45c1edd408e98ccaf84d30c3e253
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>