xen/pci: Request ACS when Xen-SWIOTLB is activated.

It used to done in the Xen startup code but that is not really
appropiate.

[v2: Update Kconfig with PCI requirement]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/xen/pci-swiotlb-xen.c

 /* Glue code to lib/swiotlb-xen.c */
 
 #include <linux/dma-mapping.h>
+#include <linux/pci.h>
 #include <xen/swiotlb-xen.h>
 
 #include <asm/xen/hypervisor.h>
@@ -54,5 +55,8 @@ void __init pci_xen_swiotlb_init(void)
 	if (xen_swiotlb) {
 		xen_swiotlb_init(1);
 		dma_ops = &xen_swiotlb_dma_ops;
+
+		/* Make sure ACS will be enabled */
+		pci_request_acs();
 	}
 }

drivers/xen/Kconfig

@@ -74,6 +74,6 @@ config XEN_PLATFORM_PCI
 
 config SWIOTLB_XEN
 	def_bool y
-	depends on SWIOTLB
+	depends on PCI && SWIOTLB
 
 endmenu