uml: create as-layout.h

This patch moves all the the symbols defined in um_arch.c, which are mostly
boundaries between different parts of the UML kernel address space, to a new
header, as-layout.h.  There are also a few things here which aren't really
related to address space layout, but which don't really have a better place to
go.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/um/kernel/um_arch.c

@@ -28,6 +28,7 @@
 #include "asm/current.h"
 #include "user_util.h"
 #include "kern_util.h"
+#include "as-layout.h"
 #include "arch.h"
 #include "kern.h"
 #include "mem_user.h"