Support GKI with non-A/B recovery

Using BOARD_PREBUILT_BOOTIMAGE instead of TARGET_NO_KERNEL to determine prebuilt boot.img.
So kernel is not excluded from recovery.img.

Bug: 187157581
Change-Id: I4163c8093c52b01d97db3cdb4f9daf840a27c23a
Test: make target-files-package
diff --git a/core/Makefile b/core/Makefile
index d8400de..bf31125 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -963,6 +963,8 @@
   $(if $(1),--partition_size $(1),--dynamic_partition_size)
 endef
 
+ifndef BOARD_PREBUILT_BOOTIMAGE
+
 ifneq ($(strip $(TARGET_NO_KERNEL)),true)
 INTERNAL_BOOTIMAGE_ARGS := \
 	$(addprefix --second ,$(INSTALLED_2NDBOOTLOADER_TARGET))
@@ -1180,7 +1182,10 @@
 endif # BUILDING_BOOT_IMAGE
 
 else # TARGET_NO_KERNEL == "true"
-ifdef BOARD_PREBUILT_BOOTIMAGE
+INSTALLED_BOOTIMAGE_TARGET :=
+endif # TARGET_NO_KERNEL
+
+else # BOARD_PREBUILT_BOOTIMAGE defined
 INTERNAL_PREBUILT_BOOTIMAGE := $(BOARD_PREBUILT_BOOTIMAGE)
 INSTALLED_BOOTIMAGE_TARGET := $(PRODUCT_OUT)/boot.img
 
@@ -1202,10 +1207,8 @@
 	cp $(INTERNAL_PREBUILT_BOOTIMAGE) $@
 endif # BOARD_AVB_ENABLE
 
-else # BOARD_PREBUILT_BOOTIMAGE not defined
-INSTALLED_BOOTIMAGE_TARGET :=
 endif # BOARD_PREBUILT_BOOTIMAGE
-endif # TARGET_NO_KERNEL
+
 endif # my_installed_prebuilt_gki_apex not defined
 
 my_apex_extracted_boot_image :=