extra: Add {AVB,Verity} signing flags

* Also move the releasekey flag to the right place, it is
  magic it ever worked as a Board-Flag.

BoardConfigExtra.mk

@@ -1,3 +1,9 @@
-# Signing
-PRODUCT_DEFAULT_DEV_CERTIFICATE := vendor/certs/releasekey
-
+## Signing
+ifeq ($(BOARD_AVB_ENABLE),true)
+BOARD_AVB_ALGORITHM := SHA256_RSA4096
+BOARD_AVB_KEY_PATH := vendor/certs/avb.pem
+ifneq ($(BOARD_AVB_SYSTEM_ROLLBACK_INDEX),)
+BOARD_AVB_SYSTEM_ALGORITHM := SHA256_RSA4096
+BOARD_AVB_SYSTEM_KEY_PATH := vendor/certs/avb.pem
+endif # BOARD_AVB_SYSTEM_ROLLBACK_INDEX
+endif # BOARD_AVB_ENABLE

product.mk

@@ -21,6 +21,11 @@ PRODUCT_COPY_FILES += \
 PRODUCT_COPY_FILES += \
     vendor/extra/adb_keys:recovery/root/adb_keys
 
+# Signing
+PRODUCT_DEFAULT_DEV_CERTIFICATE := vendor/certs/releasekey
+PRODUCT_VERITY_SIGNING_KEY := vendor/certs/verity
+
+
 ifneq ($(filter %berkeley,$(TARGET_PRODUCT)),)
 PRODUCT_PACKAGES += \
     HwCamera2