drm/msm/mdp5: Allocate CTL for each display interface

In MDP5, CTL contains information of the whole pipeline whose
output goes down to a display interface. In various cases, one
interface may require 2 CRTCs, but only one CTL. Some interfaces
also require to use certain CTLs.

Instead of allocating CTL for each active CRTC, this change is to
associate a CTL with each interface.

Signed-off-by: Hai Li <hali@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>