xen: pci: only define xen_initdom_setup_msi_irqs if CONFIG_XEN_DOM0

Fixes:
 CC      arch/x86/pci/xen.o
arch/x86/pci/xen.c:183: warning: 'xen_initdom_setup_msi_irqs' defined but not used
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

arch/x86/pci/xen.c

@@ -203,6 +203,7 @@ static void xen_teardown_msi_irq(unsigned int irq)
 	xen_destroy_irq(irq);
 }
 
+#ifdef CONFIG_XEN_DOM0
 static int xen_initdom_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
 {
 	int irq, ret;
@@ -224,6 +225,7 @@ static int xen_initdom_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
 	return ret;
 }
 #endif
+#endif
 
 static int xen_pcifront_enable_irq(struct pci_dev *dev)
 {