drm/msm/sde: add active configuration support in control path.

This change adds support for active configuration in control path.
It addresses the hw modifications to allow two interfaces to be
controlled by single control path.

Change-Id: Iac5766b3255b3a1e608af1922a2aec7967faaebd
Signed-off-by: Steve Cohen <cohens@codeaurora.org>
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>