Support arch/$ARCH/include in kbuild

[Sam Ravnborg <sam@ravnborg.org>]

Linus hinted that he liked to have all arch specific
header files moved from include/asm-$ARCH to
arch/$ARCH/include/asm.

The following two patches implement the basic support
for this.

I have used sparc for my testing and to some degree
I also used i386.

For sparc I just had to do a simple:

    mkdir -p arch/sparc/include/asm
    mv include/asm-sparc/* arch/sparc/include/asm

to build sparc with the new directory layout.

For i386 I had to do a few trivial path fixes in
arch/x86/Makefile and to fix the include of unistd_32.h
in one place to fix the build.

I expect a few additional bits to show up when people
start to move their header files but this should
be a good starting point.


To support arch/$ARCH/include/ was done in two steps.

First was to teach make headers_* about the new layout.
And second step was to get the build fixed with the new
layout.

Patches are on top of kbuild-next.git and follows.

	Sam