Set TARGET_COPY_OUT_ for product/vendor in mainline

This product variable is used to generate the loader config (to use
either /system/product or /product), and the vendor one is likely
used in similar ways. Having these partitions is required for mainline
devices, so set it in the shared BoardConfig.

Bug: 80410283
Test: make
Change-Id: I6f2d94ff43572a28df54ea8c60f2d838a3b9216c
diff --git a/target/board/BoardConfigMainlineCommon.mk b/target/board/BoardConfigMainlineCommon.mk
index ec3c74f..46e5d93 100644
--- a/target/board/BoardConfigMainlineCommon.mk
+++ b/target/board/BoardConfigMainlineCommon.mk
@@ -8,6 +8,10 @@
 
 TARGET_USERIMAGES_USE_EXT4 := true
 
+# Mainline devices must have /vendor and /product partitions.
+TARGET_COPY_OUT_VENDOR := vendor
+TARGET_COPY_OUT_PRODUCT := product
+
 # system-as-root is mandatory from Android P
 TARGET_NO_RECOVERY := true
 BOARD_BUILD_SYSTEM_ROOT_IMAGE := true