accel: Move Xen registration code to xen-common.c

Note that this has an user-visible side-effect: instead of reporting
"Xen is not supported for this target", QEMU binaries not supporting Xen
will report "xen accelerator does not exist".

As xen_available() always return 1 when CONFIG_XEN is enabled, we don't
need to set AccelClass.available anymore. xen_enabled() is not being
removed yet, but only because vl.c is still using it.

This also allows us to make xen_init() static.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/xen-common.c b/xen-common.c
index f07b35e..acc64d5 100644
--- a/xen-common.c
+++ b/xen-common.c
@@ -11,6 +11,7 @@
 #include "hw/xen/xen_backend.h"
 #include "qmp-commands.h"
 #include "sysemu/char.h"
+#include "sysemu/accel.h"
 
 //#define DEBUG_XEN
 
@@ -109,7 +110,7 @@
     }
 }
 
-int xen_init(MachineClass *mc)
+static int xen_init(MachineClass *mc)
 {
     xen_xc = xen_xc_interface_open(0, 0, 0);
     if (xen_xc == XC_HANDLER_INITIAL_VALUE) {
@@ -121,3 +122,25 @@
     return 0;
 }
 
+static void xen_accel_class_init(ObjectClass *oc, void *data)
+{
+    AccelClass *ac = ACCEL_CLASS(oc);
+    ac->name = "Xen";
+    ac->init = xen_init;
+    ac->allowed = &xen_allowed;
+}
+
+#define TYPE_XEN_ACCEL ACCEL_CLASS_NAME("xen")
+
+static const TypeInfo xen_accel_type = {
+    .name = TYPE_XEN_ACCEL,
+    .parent = TYPE_ACCEL,
+    .class_init = xen_accel_class_init,
+};
+
+static void xen_type_init(void)
+{
+    type_register_static(&xen_accel_type);
+}
+
+type_init(xen_type_init);