hwui: Don't discard framebuffer on exynos4

The layers gets empty/not cleaned and redrawn on top of the preview,
causing beautiful glitch on homescreen, and drawing black instead
of transparency.

Change-Id: I633b104224c73c625f1193ee3dde41823cddc5bf

libs/hwui/LayerRenderer.cpp

@@ -359,7 +359,7 @@ void LayerRenderer::destroyLayerDeferred(Layer* layer) {
 }
 
 void LayerRenderer::flushLayer(Layer* layer) {
-#ifdef GL_EXT_discard_framebuffer
+#if defined(GL_EXT_discard_framebuffer) && !defined(EXYNOS4_ENHANCEMENTS)
     GLuint fbo = layer->getFbo();
     if (layer && fbo) {
         // If possible, discard any enqueud operations on deferred