build: in new image building code, do not rebuild kernel images in the image builder

Some kernel images need to be wrapped in a loader, which cannot be built
without a working toolchain.
Also, this speeds up the image builder run.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 45836

include/image.mk

@@ -397,10 +397,15 @@ define Device/Build/kernel
   $$(_TARGET): $$(if $$(KERNEL_INSTALL),$(BIN_DIR)/$$(KERNEL_IMAGE))
   $(BIN_DIR)/$$(KERNEL_IMAGE): $(KDIR)/$$(KERNEL_IMAGE)
 	cp $$^ $$@
-  $(KDIR)/$$(KERNEL_IMAGE): $(KDIR)/$$(KERNEL_NAME)
+  ifndef IB
+    ifdef CONFIG_IB
+      install: $(KDIR)/$$(KERNEL_IMAGE)
+    endif
+    $(KDIR)/$$(KERNEL_IMAGE): $(KDIR)/$$(KERNEL_NAME)
 	@rm -f $$@
 	$$(call concat_cmd,$$(KERNEL))
 	$$(if $$(KERNEL_SIZE),$$(call Device/Build/check_size,$$(KERNEL_SIZE)))
+  endif
 endef
 
 define Device/Build/image