hwc: Query MDP capability for blending stages supported.

- Read MDP sys_fs node for blending stages supported per mixer
  instead of hard cording the value. This makes the implementation
  scalable across chipsets.
- Add binder support to change the max pipes per layer value
  dynamically for MDP comp.

Change-Id: I3b83f4bdc2e2e81ca55c54fc6bcfd61c55fef501
diff --git a/libqservice/IQService.h b/libqservice/IQService.h
index 87d51fc..6f2f0e3 100644
--- a/libqservice/IQService.h
+++ b/libqservice/IQService.h
@@ -50,7 +50,7 @@
         SET_HSIC_DATA,           // Set HSIC on dspp
         GET_DISPLAY_VISIBLE_REGION,  // Get the visibleRegion for dpy
         SET_SECONDARY_DISPLAY_STATUS,  // Sets secondary display status
-        UNUSED_SLOT,             // XXX: Unsed - New one can go here
+        SET_MAX_PIPES_PER_MIXER, // Set max pipes per mixer for MDPComp
         SET_VIEW_FRAME,          // Set view frame of display
         DYNAMIC_DEBUG,           // Enable more logging on the fly
         SET_IDLE_TIMEOUT,        // Set idle timeout for GPU fallback