Invoke a padding round in certain use-cases.

* In some use-cases, it is possible that there are
no AppBuffer layers on the external/virtual layer-list
during which all the pipes will be allocated to the
primary. When layers do comeup on external/virtual
layer-list, subsequent overlay sets fail.

* This change ensures that in such cases, we invoke a
padding round on all the displays to free up the
hw resources which can be used in subsequent cycles.

Change-Id: Ifac0b8f51a8719eb55b11010d05b8d11352db054

libhwcomposer/hwc_utils.cpp

@@ -213,6 +213,10 @@ void initContext(hwc_context_t *ctx)
         ctx->dpyAttr[i].mAsHeightRatio = 0;
     }
 
+    for (uint32_t i = 0; i < HWC_NUM_DISPLAY_TYPES; i++) {
+        ctx->mPrevHwLayerCount[i] = 0;
+    }
+
     MDPComp::init(ctx);
     ctx->mAD = new AssertiveDisplay(ctx);
 
@@ -897,6 +901,7 @@ void setListStats(hwc_context_t *ctx,
     if(prevYuvCount != ctx->listStats[dpy].yuvCount) {
         ctx->mVideoTransFlag = true;
     }
+
     if(dpy == HWC_DISPLAY_PRIMARY) {
         ctx->mAD->markDoable(ctx, list);
     }