aosp_arm64 Copy boot image from $OUT to target files

If BOARD_COPY_BOOT_IMAGE_TO_TARGET_FILES is defined,
in target files, instead of rebuilding the boot image, copy the boot
image already built in $OUT to target files package directly so that
they are the same package.

Define BOARD_COPY_BOOT_IMAGE_TO_TARGET_FILES for aosp_arm64.

The GKI APEX is built using the boot image in $OUT. If the boot image in
$OUT is different from the boot image in target files, aka the generic
boot image we release, the GKI APEX we built is invalid.

If another device needs to copy $OUT/boot.img to target files, it can
define BOARD_COPY_BOOT_IMAGE_TO_TARGET_FILES.

Fixes: 172682114
Test: lunch aosp_arm64 &&
Change-Id: I10fc7a5aa36e976dbeaf25434239687455bba061
diff --git a/core/board_config.mk b/core/board_config.mk
index 457b3bf..bc52345 100644
--- a/core/board_config.mk
+++ b/core/board_config.mk
@@ -107,11 +107,14 @@
 #   recovery resources are built to vendor_boot.
 # - BOARD_MOVE_GSI_AVB_KEYS_TO_VENDOR_BOOT controls whether GSI AVB keys are
 #   built to vendor_boot.
+# - BOARD_COPY_BOOT_IMAGE_TO_TARGET_FILES controls whether boot images in $OUT are added
+#   to target files package directly.
 _board_strip_readonly_list += \
   BOARD_USES_GENERIC_KERNEL_IMAGE \
   BOARD_EXCLUDE_KERNEL_FROM_RECOVERY_IMAGE \
   BOARD_MOVE_RECOVERY_RESOURCES_TO_VENDOR_BOOT \
   BOARD_MOVE_GSI_AVB_KEYS_TO_VENDOR_BOOT \
+  BOARD_COPY_BOOT_IMAGE_TO_TARGET_FILES \
 
 _build_broken_var_list := \
   BUILD_BROKEN_DUP_RULES \