drivers: thermal: Add a new DDR cooling device

Add a new DDR cooling device which can request for a DDR state as a part
of cooling device request. This will help in the situation where DDR has
to be kept at a specific state during thermally constrained situations.

Change-Id: Ic1108cc86424c03e7cb176d595c534e5905c103a
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>