Make sure all HWC2 functionality is ifdef'd

Fix build issue for devices that are not using HWC2.
Test: lunch bat_land, make

Change-Id: If94222cd00f2c8b0b1f7a464ad0378224fc059e7
(cherry picked from commit ebeed4917b6a341a6287141f3755a750ab4431cb)
diff --git a/services/surfaceflinger/DisplayDevice.cpp b/services/surfaceflinger/DisplayDevice.cpp
index 976455e..87c4ea7 100644
--- a/services/surfaceflinger/DisplayDevice.cpp
+++ b/services/surfaceflinger/DisplayDevice.cpp
@@ -114,7 +114,9 @@
       mOrientation(),
       mPowerMode(HWC_POWER_MODE_OFF),
       mActiveConfig(0),
+#ifdef USE_HWC2
       mDisplayHasWideColor(supportWideColor)
+#endif
 {
     // clang-format on
     Surface* surface;