cm: Update use of vendor/extra `

 * Use inherit-product to pick up extra configuration

Change-Id: Icb0c8b09cd10b503e2dca09b7a972a613c354e7d
diff --git a/config/common.mk b/config/common.mk
index 3c3e59f..12945af 100644
--- a/config/common.mk
+++ b/config/common.mk
@@ -231,9 +231,6 @@
 
 endif
 
-# easy way to extend to add more packages
--include vendor/extra/product.mk
-
 PRODUCT_PACKAGE_OVERLAYS += vendor/cm/overlay/common
 
 PRODUCT_VERSION_MAJOR = 11
@@ -344,3 +341,5 @@
 -include $(WORKSPACE)/build_env/image-auto-bits.mk
 
 -include vendor/cyngn/product.mk
+
+$(call inherit-product-if-exists, vendor/extra/product.mk)