Mini-OS: standalone build

In order to keep the tree bisectable all the changes are done in one
single commit.

Things done in this commit:

1. Import necessary .mk files from Xen.
2. Move all XEN_ related variables to MINIOS_ namespace.
3. Import Xen public header files.
4. Import BSD's list.h and helper script.

Mini-OS's vanilla Config.mk is modified to contain some macros copied
from Xen's Config.mk. It also contains compatibility handling logic for
Xen's stubdom build environment.

Files modified:
   Config.mk
   Makefile
   arch/x86/Makefile
   arch/x86/arch.mk
   minios.mk

All other files are just imported from Xen.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

.gitignore

@@ -48,7 +48,6 @@ docs/pdf/
 docs/txt/
 extras/mini-os/include/mini-os
 extras/mini-os/include/x86/mini-os
-extras/mini-os/include/xen
 extras/mini-os/include/list.h
 extras/mini-os/mini-os*
 install/*