Minor cleanups/fixes before virtual display refactoring

None of these should change behavior, except for removing some
incorrect log messages when using a virtual display.

- HWComposer::getAndResetReleaseFenceFd() checks the HWC version, so
  no need to do that in the DisplayDevice::onSwapBuffersCompleted().
  However, it should check that mFramebufferSurface is not NULL like
  it is for virtual displays.
- Comment that FramebufferSurface::dump() overrides the non-virtual
  ConsumerBase::dump(), and fix it so the right thing happens
  regardless of the static type of the pointer/reference the callee
  has. FramebufferSurface::dump() could be removed right now, but I'd
  need to bring it back in a later change.
- Use the right enum for validating display type ids.
- Don't try to send hotplug events for virtual displays.
- Mark virtual displays as connected so HWComposer::prepare() doesn't
  think something is wrong when it gets a non-NULL layer list.
- Remove unused FramebufferSurface methods.

Bug: 8384764
Change-Id: Id28a2f9be86b45f4bb7915fdf7752157035f4294
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 98f6ded..551f902 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -1131,7 +1131,8 @@
                         DisplayDevice::makeCurrent(mEGLDisplay, hw, mEGLContext);
                         mDisplays.removeItem(draw.keyAt(i));
                         getHwComposer().disconnectDisplay(draw[i].type);
-                        mEventThread->onHotplugReceived(draw[i].type, false);
+                        if (draw[i].type < DisplayDevice::NUM_DISPLAY_TYPES)
+                            mEventThread->onHotplugReceived(draw[i].type, false);
                     } else {
                         ALOGW("trying to remove the main display");
                     }
@@ -1204,7 +1205,8 @@
                                 state.viewport, state.frame);
                         hw->setDisplayName(state.displayName);
                         mDisplays.add(display, hw);
-                        mEventThread->onHotplugReceived(state.type, true);
+                        if (state.type < DisplayDevice::NUM_DISPLAY_TYPES)
+                            mEventThread->onHotplugReceived(state.type, true);
                     }
                 }
             }