overlay: Add writeback support

Add explicit writeback display type, writeback ioctls, memory mgmt,
writeback class, writeback obj manager class to overlay.

Change-Id: I171e60cea5ed8f6649859e3eb189df37b39962f1
diff --git a/libhwcomposer/hwc.cpp b/libhwcomposer/hwc.cpp
index e322357..1439578 100644
--- a/libhwcomposer/hwc.cpp
+++ b/libhwcomposer/hwc.cpp
@@ -28,6 +28,7 @@
 #include <sys/ioctl.h>
 #include <overlay.h>
 #include <overlayRotator.h>
+#include <overlayWriteback.h>
 #include <mdp_version.h>
 #include "hwc_utils.h"
 #include "hwc_fbupdate.h"
@@ -214,6 +215,8 @@
 
     ctx->mOverlay->configBegin();
     ctx->mRotMgr->configBegin();
+    overlay::Writeback::configBegin();
+
     Overlay::setDMAMode(Overlay::DMA_LINE_MODE);
 
     for (int32_t i = numDisplays; i >= 0; i--) {
@@ -233,6 +236,7 @@
 
     ctx->mOverlay->configDone();
     ctx->mRotMgr->configDone();
+    overlay::Writeback::configDone();
 
     return ret;
 }
@@ -285,6 +289,7 @@
         ctx->mOverlay->configBegin();
         ctx->mOverlay->configDone();
         ctx->mRotMgr->clear();
+        overlay::Writeback::clear();
     }
     switch(dpy) {
         case HWC_DISPLAY_PRIMARY: