drm/msm/sde: expose ad4 interface to clients

if sde supports assertive display block user-space clients can use the
interface exposed to program the block. Change creates an interface for
ad4 parameters.

Change-Id: Icf115a91397991f4498d39c657a8841065558450
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>