xen: add xen hvm acpi_register_gsi variant

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
index 08e3cdc..3a4ab0b 100644
--- a/arch/x86/pci/xen.c
+++ b/arch/x86/pci/xen.c
@@ -53,6 +53,12 @@
 
 	return irq;
 }
+
+static int acpi_register_gsi_xen_hvm(struct device *dev, u32 gsi,
+				 int trigger, int polarity)
+{
+	return xen_hvm_register_pirq(gsi, trigger);
+}
 #endif
 
 #if defined(CONFIG_PCI_MSI)