regulator: cpr-regulator: Add support for Voltage Sensors

Voltage sensor regulators need to be notified when the corner of apc
rail changes. Voltage Sensor regulator needs to be disabled prior
to changing the apc corner and needs to be notified of the ceiling
and floor voltage before enabling it again.

Change-Id: I0156480f6bfaf10397578caded2c15a298f20f95
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>