power: pm8xxx-ccadc: implement quick calibration

There are certain systems that wakeup every so often to do some
housekeeping work. We don't want to run a full calibration
when the system wakeups.

For such systems runs a quick calibration with just two samples.
Use the periodic_wakeup flag to indicate such a system.

CRs-Fixed: 454221
Change-Id: Ifc86414f7fab4d0921e3289d6e52b9e077a1f625
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>