Don't build retrofit OTA package if vendor.img is unavailable.

We used to build retrofit full OTA package as long as
PRODUCT_RETROFIT_DYNAMIC_PARTITIONS is true. This doesn't work with AOSP
targets that have the flag set but without any available vendor image.

This CL detects such a condition and uses a separate flag to guard the
retrofit OTA building as well as the split super images generation.

Bug: 120852744
Test: `m -j dist` on blueline (w/ vendor images) and aosp_blueline (w/o
      vendor images).
Change-Id: I65726f24f8fc546be6802941a6a06590a3804c16
diff --git a/core/Makefile b/core/Makefile
index 1b2b704..06ac70e 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -3426,6 +3426,8 @@
   echo "lpmake=$(notdir $(LPMAKE))" >> $(1)
   $(if $(filter true,$(PRODUCT_BUILD_SUPER_PARTITION)), $(if $(BOARD_SUPER_PARTITION_SIZE), \
     echo "build_super_partition=true" >> $(1)))
+  $(if $(filter true,$(BOARD_BUILD_RETROFIT_DYNAMIC_PARTITIONS_OTA_PACKAGE)), \
+    echo "build_retrofit_dynamic_partitions_ota_package=true" >> $(1))
   echo "super_metadata_device=$(BOARD_SUPER_PARTITION_METADATA_DEVICE)" >> $(1)
   $(if $(BOARD_SUPER_PARTITION_BLOCK_DEVICES), \
     echo "super_block_devices=$(BOARD_SUPER_PARTITION_BLOCK_DEVICES)" >> $(1))
@@ -3886,7 +3888,7 @@
 .PHONY: otapackage
 otapackage: $(INTERNAL_OTA_PACKAGE_TARGET)
 
-ifeq ($(PRODUCT_RETROFIT_DYNAMIC_PARTITIONS),true)
+ifeq ($(BOARD_BUILD_RETROFIT_DYNAMIC_PARTITIONS_OTA_PACKAGE),true)
 name := $(TARGET_PRODUCT)
 ifeq ($(TARGET_BUILD_TYPE),debug)
   name := $(name)_debug
@@ -3912,7 +3914,7 @@
 
 otapackage otardppackage: $(INTERNAL_OTA_RETROFIT_DYNAMIC_PARTITIONS_PACKAGE_TARGET)
 
-endif # PRODUCT_RETROFIT_DYNAMIC_PARTITIONS
+endif # BOARD_BUILD_RETROFIT_DYNAMIC_PARTITIONS_OTA_PACKAGE
 
 endif    # build_ota_package