Switch to 3 FramebufferSurface buffers

Changes from 2 to 3 FramebufferSurface buffers to avoid tearing
because of invalid fence semantics. This is a hack (but a useful one).

Bug: 37207024
Test: Rotate device and notice no tearing; force GL composition and
      drag an item in recents up and down quickly to also notice no
      tearing

Change-Id: I58fa2feac0802a6bd2cd91a1e9fd41ee387de1f2
diff --git a/BoardConfig.mk b/BoardConfig.mk
index 0ae04ec..9355977 100644
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -91,6 +91,7 @@
 MAX_VIRTUAL_DISPLAY_DIMENSION := 2048
 VSYNC_EVENT_PHASE_OFFSET_NS := 2000000
 SF_VSYNC_EVENT_PHASE_OFFSET_NS := 6000000
+NUM_FRAMEBUFFER_SURFACE_BUFFERS := 3
 
 
 TARGET_AUX_OS_VARIANT_LIST := bullhead