Add BUILD_RECOVERY_IMAGE and BUILD_BOOT_IMAGE flags

Bug: 123428770
Test: Built system-only image and checked that no boot.img or
recovery.img files where created. Booted the resulting merged build on
device.

Change-Id: I760476502775e68125907c39e66b8665e789a798

core/product_config.mk

@@ -405,7 +405,9 @@ $(foreach image, \
     ODM \
     CACHE \
     RAMDISK \
-    USERDATA, \
+    USERDATA \
+    BOOT \
+    RECOVERY, \
   $(eval $(call product-build-image-config,$(image))))
 
 product-build-image-config :=