The top-level Makefile is separated into two parts, one which does
include .config, so it can access CONFIG_FOO, and one which does not,
since it may not even exist yet (make *config).

However, both parts need to include arch/$(ARCH)/Makefile, be it for 
arch-specific settings or just for archclean/archmrproper.

So we now include arch/$(ARCH)/Makefile before the config/noconfig split,
which also has the advantage of giving us the arch-specific build dirs
(e.g. arch/i386/{kernel,mm,lib}) in both cases.

In addition, fix a couple of small glitches (make menuconfig, make 
modules_install, proper output when descending)