xics-kvm: enable irqfd for MSI

This enables IRQFD support for sPAPR. The feature decreases the latency
of interrupt handling.

To enable IRQFD for MSI, this sets kvm_gsi_direct_mapping to true which
enables direct MSI mapping.

To enable IRQFD for LSI (level triggered INTx interrupts), a PCI host bus
callback is required. The patch for that is coming next.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alexander Graf <agraf@suse.de>

hw/intc/xics_kvm.c

@@ -441,6 +441,12 @@ static void xics_kvm_realize(DeviceState *dev, Error **errp)
             goto fail;
         }
     }
+
+    kvm_kernel_irqchip = true;
+    kvm_irqfds_allowed = true;
+    kvm_msi_via_irqfd_allowed = true;
+    kvm_gsi_direct_mapping = true;
+
     return;
 
 fail: