display: msm: sde: Add display cooling device interface

Add display cooling device interface, which will enable to register a
cooling device and send a blocking notifier call when there is a new
mitigation request.

Change-Id: I59e4a7190f637fba7f63e47ff495242718cc3c9b
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>