kbuild: More "make clean" cosmetics

Make the DocBook "make clean" output nicer and use the fast variant
for arch/i386/boot as well.

Documentation/DocBook/Makefile

@@ -160,7 +160,8 @@ clean-files := $(DOCBOOKS) \
 	$(patsubst %.fig,%.png, $(IMG-parportbook)) \
 	$(C-procfs-example)
 
-clean-rule := rm -rf $(patsubst %.html,%,$(HTML))
+ifneq ($(wildcard $(BOOKS)),)
+clean-rule := rm -rf $(wildcard $(BOOKS))
+endif
 
 include $(TOPDIR)/Rules.make
-

arch/i386/Makefile

@@ -88,6 +88,6 @@ install: vmlinux
 	+@$(call makeboot,BOOTIMAGE=$(BOOTIMAGE) install)
 
 archclean:
-	+@$(call makeboot,subdirclean)
+	$(MAKE) -rR -f scripts/Makefile.clean obj=arch/i386/boot
 
 archmrproper: