fix [3312683] Camera mirroring problem after switching from back to front camera

the crop as well as buffer orientation can change at every frame, when that happens
we need to reset the hwc HAL (ie: set the GEOMETRY_CHANGED flag).
currently we achieve this by taking the same code path than an actual geometry change
which is a bit more heavy than necessary.

Change-Id: I751f9ed1eeec0c27db7df2e77d5d17c6bcc17a24
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index 48642d4..0729879 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -208,6 +208,7 @@
     status_t removeLayer(const sp<LayerBase>& layer);
     status_t addLayer(const sp<LayerBase>& layer);
     status_t invalidateLayerVisibility(const sp<LayerBase>& layer);
+    void invalidateHwcGeometry();
 
     sp<Layer> getLayer(const sp<ISurface>& sur) const;