test-hwc2: virtual displays

Test: Add "#define HAVE_NO_SURFACE_FLINGER" to
      frameworks/native/libs/gui/BufferQueueCore.cpp.
      Recompile and flash.
      Run "mm" in frameworks/native/services/surfaceflinger/tests/hwc2.
      Push test-hwc2 to device.
      Run "adb root && adb shell stop".
      Run test case. Ex: "./test-hwc2"

Change-Id: Ia10ec761712ee03f56782e3df2d6eabf7fb77760