hw/xen: Implement emulated PIRQ hypercall support

This wires up the basic infrastructure but the actual interrupts aren't
there yet, so don't advertise it to the guest.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
diff --git a/meson.build b/meson.build
index 71a14e6..e533d6c 100644
--- a/meson.build
+++ b/meson.build
@@ -2982,6 +2982,7 @@
     'hw/i2c',
     'hw/i386',
     'hw/i386/xen',
+    'hw/i386/kvm',
     'hw/ide',
     'hw/input',
     'hw/intc',