build_image.py recognize BOARD_PRODUCTIMAGE_PARTITION_RESERVED_SIZE

Test: builds
Bug: 79106666
Change-Id: I26aba694fd3d6a2feed7601524dde52569ba41e2
diff --git a/core/config.mk b/core/config.mk
index f7a8176..81ca30c 100644
--- a/core/config.mk
+++ b/core/config.mk
@@ -931,6 +931,13 @@
 endif
 endif
 
+ifneq ($(BOARD_PRODUCTIMAGE_PARTITION_SIZE),)
+ifneq ($(BOARD_PRODUCTIMAGE_PARTITION_RESERVED_SIZE),)
+$(error Should not define BOARD_PRODUCTIMAGE_PARTITION_SIZE and \
+    BOARD_PRODUCTIMAGE_PARTITION_RESERVED_SIZE together)
+endif
+endif
+
 endif # USE_LOGICAL_PARTITIONS
 
 # ###############################################################