meson: convert hw/xen

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/hw/meson.build b/hw/meson.build
new file mode 100644
index 0000000..08112a5
--- /dev/null
+++ b/hw/meson.build
@@ -0,0 +1 @@
+subdir('xen')