drm/msm: handle drm lastclose using downstream msm API

Use downstream API "msm_lastclose", instead of the
upstream one "drm_fb_helper_lastclose" to service msm
driver lastclose function pointer. Downstream API ensures
that objects and custom properties are cleared and internally
committed when the driver is closed.

Change-Id: Icf356ac47c15afb6ad7d0a62d96c06eb78c074f1
Signed-off-by: Amine Najahi <anajahi@codeaurora.org>