hwc/overlay: Fix dma mode design and issues.

Add support for tracking the mode in which DMA is being used in overlay.
Remove unnecessary tracking variables, and their set,reset inconsistency.

With such varibles in hwc, it still leads to overlay giving out DMA pipes.
Make overlay as the single tracking place.

Change-Id: Ib949f3d0ef5918ef323c81cb1768b68a68c83da4

libhwcomposer/hwc.cpp

@@ -38,6 +38,8 @@
 #include "profiler.h"
 
 using namespace qhwc;
+using namespace overlay;
+
 #define VSYNC_DEBUG 0
 #define BLANK_DEBUG 0
 
@@ -200,7 +202,7 @@ static int hwc_prepare(hwc_composer_device_1 *dev, size_t numDisplays,
 
     ctx->mOverlay->configBegin();
     ctx->mRotMgr->configBegin();
-    ctx->mNeedsRotator = false;
+    Overlay::setDMAMode(Overlay::DMA_LINE_MODE);
 
     for (int32_t i = numDisplays; i >= 0; i--) {
         hwc_display_contents_1_t *list = displays[i];