surfaceflinger: add RenderEngine::mEGLDisplay

It does not make much sense to have EGLConfig/EGLContext but not
EGLDisplay in RenderEngine.  We also need this as we move forward on
making EGL an implementation detail of RenderEngine.

Test: SurfaceFlinger_test
Change-Id: I9e2c9b9817e2c2a9b2555ea575be6dcd91927b79
diff --git a/services/surfaceflinger/DisplayDevice.cpp b/services/surfaceflinger/DisplayDevice.cpp
index 6d6781e..a9f3aa1 100644
--- a/services/surfaceflinger/DisplayDevice.cpp
+++ b/services/surfaceflinger/DisplayDevice.cpp
@@ -120,7 +120,8 @@
      */
 
     EGLSurface eglSurface;
-    EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
+    EGLDisplay display = mFlinger->getRenderEngine().getEGLDisplay();
+
     if (config == EGL_NO_CONFIG) {
         config = RenderEngine::chooseEglConfig(display, PIXEL_FORMAT_RGBA_8888,
                                                /*logConfig*/ false);