x86: use unified linker script

x86: use unified linker script

There are only a few differences between i386 and x86-64 linker scripts.
Unify them into one. Re-indent the file at the same time.

Construct a special rule in top-level directory to cope with the change.
Ideally the build system should also be made more elegant, but
overhauling the build system is out of scope of this patch.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: Samuel Thibault <samuel.thibault@ens-lyon.org>