Move eglSwapBuffers out of HWComposer

Commit 8630320 moved the eglSwapBuffers fallback (for devices with no
HWC implementation) from DisplayHardware to HWComposer. But HWComposer
only knows about the framebuffer EGL display and surface handles if
there is a HWC, so it was always passing bogus handles.

This change moves the eglSwapBuffers fallback up to SurfaceFlinger,
which has access to the framebuffer EGL handles.

Bug: 6886613
Change-Id: Iad3f5ff7c90ee48d7053999e6a4548d6794b6ebd
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index c33f1a3..a3d8538 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -390,6 +390,7 @@
     GLint mMaxTextureSize;
     EGLContext mEGLContext;
     EGLConfig mEGLConfig;
+    EGLDisplay mEGLDisplay;
 
     // Can only accessed from the main thread, these members
     // don't need synchronization