libqservice: Defer enabling partial update PP turns off

When client prefer to enable PU(partial update) over PP(post
processing), delay enabling PU until PP turns off its
features completely. This change introduces hand shaking flags
between PP and HWC through binder calls. When requested to turn
on PU, we notify PP through the sys_fs node. When PP is done
shutting off it features, it acknowledges back to HWC to actually
turn on PU.

Change-Id: I72008f2313b93497f55c0435367ef62cd772c2c4
diff --git a/libhwcomposer/hwc_mdpcomp.h b/libhwcomposer/hwc_mdpcomp.h
index a83f51f..7752384 100644
--- a/libhwcomposer/hwc_mdpcomp.h
+++ b/libhwcomposer/hwc_mdpcomp.h
@@ -58,6 +58,8 @@
     static void setMaxPipesPerMixer(const uint32_t value);
     static int setPartialUpdatePref(hwc_context_t *ctx, bool enable);
     static bool getPartialUpdatePref(hwc_context_t *ctx);
+    static void enablePartialUpdate(bool enable)
+                                          { sIsPartialUpdateActive = enable; };
     void setDynRefreshRate(hwc_context_t *ctx, hwc_display_contents_1_t* list);
 
 protected: