cm: Include private signing keys if present

Change-Id: Ic96d4d49d821cb03d5318e3e9ad93d02fb92573e
diff --git a/config/common.mk b/config/common.mk
index 9eb86b1..33ba366 100644
--- a/config/common.mk
+++ b/config/common.mk
@@ -1,5 +1,6 @@
 PRODUCT_BRAND ?= cyanogenmod
 
+-include vendor/cm-priv/keys.mk
 SUPERUSER_EMBEDDED := true
 SUPERUSER_PACKAGE_PREFIX := com.android.settings.cyanogenmod.superuser