kbuild: fix help output to show correct arch

	@echo  'Documentation targets:'

	@$(MAKE) -f $(srctree)/Documentation/DocBook/Makefile dochelp

	@echo  ''

	@echo  'Architecture specific targets ($(ARCH)):'

	@echo  'Architecture specific targets ($(SRCARCH)):'

	@$(if $(archhelp),$(archhelp),\

		echo '  No architecture specific help defined for $(ARCH)')

		echo '  No architecture specific help defined for $(SRCARCH)')

	@echo  ''

	@$(if $(boards), \

		$(foreach b, $(boards), \