Make AVB work when BOARD_USES_RECOVERY_AS_BOOT is set to true.

Often BOARD_USES_RECOVERY_AS_BOOT is used together with
BOARD_BUILD_SYSTEM_ROOT_IMAGE, but with this combination we're
currently not adding a hash footer to boot.img. Fix this.

Bug: 31119415
Test: aosp_x86_64-eng 'm' and 'm dist' successful.
Change-Id: If033e5c93f5b71fd17405af7d970dc3f0540a1d2
diff --git a/core/Makefile b/core/Makefile
index b649b0c..85942e8 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -1052,6 +1052,12 @@
   )
   $(if $(filter true,$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_VBOOT)), \
     $(VBOOT_SIGNER) $(FUTILITY) $(1).unsigned $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_VBOOT_SIGNING_KEY).vbpubk $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_VBOOT_SIGNING_KEY).vbprivk $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_VBOOT_SIGNING_SUBKEY).vbprivk $(1).keyblock $(1))
+  $(if $(and $(filter true,$(BOARD_USES_RECOVERY_AS_BOOT)),$(filter true,$(BOARD_AVB_ENABLE))), \
+      $(hide) $(AVBTOOL) add_hash_footer \
+        --image $(1) \
+        --partition_size $(BOARD_BOOTIMAGE_PARTITION_SIZE) \
+        --partition_name boot $(INTERNAL_AVB_SIGNING_ARGS) \
+        $(BOARD_AVB_BOOT_ADD_HASH_FOOTER_ARGS))
   $(if $(filter true,$(BOARD_USES_RECOVERY_AS_BOOT)), \
     $(hide) $(call assert-max-image-size,$(1),$(BOARD_BOOTIMAGE_PARTITION_SIZE)), \
     $(hide) $(call assert-max-image-size,$(1),$(BOARD_RECOVERYIMAGE_PARTITION_SIZE)))