add a hook to add extra packages

Change-Id: I1f955a59a18bda22c4431d05a426aab91764d20d

Conflicts:
	config/common.mk
diff --git a/config/common.mk b/config/common.mk
index 928834e..b303e8b 100644
--- a/config/common.mk
+++ b/config/common.mk
@@ -102,6 +102,9 @@
     mke2fs \
     tune2fs
 
+# easy way to extend to add more packages
+-include vendor/extra/product.mk
+
 PRODUCT_PACKAGE_OVERLAYS += vendor/slim/overlay/common
 
 # Boot animation include