Make build support vendor_kernel_boot image

Add vendor_kernel_boot image for vendors whose bootloader support
extra first stage booting kernel modules ramdisks. This benefit
kernel repo to build kernel-artifacts only image without Andorid
artifacts dependency.

Bug: 214409109
Signed-off-by: Lucas Wei <lucaswei@google.com>
Change-Id: If07218b86a7751b3d452a172610af960f5f9ec74
diff --git a/core/envsetup.mk b/core/envsetup.mk
index 5c5b565..8f70e57 100644
--- a/core/envsetup.mk
+++ b/core/envsetup.mk
@@ -282,6 +282,7 @@
 _system_dlkm_path_placeholder := ||SYSTEM_DLKM-PATH-PH||
 TARGET_COPY_OUT_VENDOR := $(_vendor_path_placeholder)
 TARGET_COPY_OUT_VENDOR_RAMDISK := vendor_ramdisk
+TARGET_COPY_OUT_VENDOR_KERNEL_RAMDISK := vendor_kernel_ramdisk
 TARGET_COPY_OUT_PRODUCT := $(_product_path_placeholder)
 # TODO(b/135957588) TARGET_COPY_OUT_PRODUCT_SERVICES will copy the target to
 # product
@@ -988,6 +989,7 @@
 .KATI_READONLY := TARGET_SYSTEM_DLKM_OUT
 
 TARGET_VENDOR_RAMDISK_OUT := $(PRODUCT_OUT)/$(TARGET_COPY_OUT_VENDOR_RAMDISK)
+TARGET_VENDOR_KERNEL_RAMDISK_OUT := $(PRODUCT_OUT)/$(TARGET_COPY_OUT_VENDOR_KERNEL_RAMDISK)
 
 TARGET_ROOT_OUT := $(PRODUCT_OUT)/$(TARGET_COPY_OUT_ROOT)
 TARGET_ROOT_OUT_BIN := $(TARGET_ROOT_OUT)/bin