drivers: msm-pm: Add SPC flag for standalone power collapse

Use mode flag to distinguish between standalone power collapse
and power collapse sequence.

Change-Id: Idfa3586d0c06e8c6d9e922747438dfb109a8213a
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>
Signed-off-by: Archana Sathyakumar <asathyak@codeaurora.org>