drm/msm: Expose Assertive display capability

During probe the assertive display capability is read by the post
processing module from device tree/catalog. If chipset supports the
feature, an immutable property is created and exposed to user.

Change-Id: I7b39537b49a6efe346bdf5a0d0697c5875c8d2f7
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>