Refactor build for grouper.

Change-Id: I52c16e1f050279431528e43c73627e73abf95462
diff --git a/BoardConfigCommon.mk b/BoardConfigCommon.mk
index 504efe7..d515120 100644
--- a/BoardConfigCommon.mk
+++ b/BoardConfigCommon.mk
@@ -76,3 +76,5 @@
 NEED_WORKAROUND_CORTEX_A9_745320 := true
 
 TARGET_RELEASETOOLS_EXTENSIONS := device/asus/grouper
+
+BOARD_USES_GROUPER_MODULES := true