gs101: use prebuilt GKI boot.img for production builds

Use prebuilt GKI boot.img for production builds.
Debug builds continue to use their own Image.lz4.

Bug: 191764119
Change-Id: I2b4950ce334cc990e858e0ea410ad7e57d6decf6
diff --git a/BoardConfig-common.mk b/BoardConfig-common.mk
index ba119b9..cff6ed2 100644
--- a/BoardConfig-common.mk
+++ b/BoardConfig-common.mk
@@ -53,8 +53,13 @@
 BOARD_BOOTCONFIG += androidboot.boot_devices=14700000.ufs
 
 TARGET_NO_BOOTLOADER := true
-TARGET_NO_KERNEL := false
 TARGET_NO_RADIOIMAGE := true
+ifeq (,$(TARGET_PREBUILT_KERNEL))
+TARGET_NO_KERNEL := true
+BOARD_PREBUILT_BOOTIMAGE := $(TARGET_KERNEL_DIR)/boot.img
+else
+TARGET_NO_KERNEL := false
+endif
 BOARD_USES_GENERIC_KERNEL_IMAGE := true
 BOARD_MOVE_RECOVERY_RESOURCES_TO_VENDOR_BOOT := true
 BOARD_MOVE_GSI_AVB_KEYS_TO_VENDOR_BOOT := true