drivers: thermal: sdpm: Add support for regulator notification

Register for regulator enable and disable notification for certain
SDPMs. This will ensure that we vote for a frequency value of zero when
the regulator is disabled. So even if the client wont vote for a lower
frequency value and then disable the clock, the regulator notification
will help in detecting this scenario.

Change-Id: I7aa9704858e83c66fcd68512dd29ed7f50e4e321
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>