Revert part of Xen/x86/PCI: Add support for the Xen PCI subsystem

The original patch "Xen/x86/PCI: Add support for the Xen PCI subsystem"
contains iommu feature. But when some of this patch is not picked. So
revert these not picked changes. 

 Not picked:
        drivers/pci/Makefile
        drivers/pci/xen-iommu.c
        arch/x86/kernel/pci-dma.c
        arch/x86/include/asm/xen/iommu.h

=======
 From a8a5c674958a994c034fe83e31e6ee5517334a34 Mon Sep 17 00:00:00 2001
 From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
 Date: Mon, 1 Mar 2010 18:17:08 -0500
 Subject: [PATCH] Xen/x86/PCI: Add support for the Xen PCI subsystem

 This is based on an earlier version of this commit (
 b61bf14130a290deccc3a94e104a394e318fc595), but with the IOMMU
 code removed.

 The frontend stub lives in arch/x86/pci-xen.c, alongside other
 sub-arch PCI init code (e.g. olpc.c)


 [ Impact: add core of Xen PCI support ]

 Signed-off-by: Alex Nixon <alex.nixon@citrix.com>
 Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
 Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
 Reviewed-by: "H. Peter Anvin" <hpa@zytor.com>
 Reviewed-by: Matthew Wilcox <willy@linux.intel.com>

 Conflicts:

        arch/x86/include/asm/io.h

 Not picked:
        drivers/pci/Makefile
        drivers/pci/xen-iommu.c
        arch/x86/kernel/pci-dma.c
        arch/x86/include/asm/xen/iommu.h


Signed-off-by: Charles Wang <muming.wq@taobao.com>