kvmclock: Remove user_creatable flag

kvmclock should be used by guests only when the appropriate CPUID
feature flags are set on the VCPU, and it is automatically
created by kvmclock_create() when those feature flags are set.
This means creating a kvmclock device using -device is useless.
Remove user_creatable from its device class.

Cc: Marcel Apfelbaum <marcel@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Thomas Huth <thuth@redhat.com>
Acked-by: NMarcel Apfelbaum <marcel@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Message-Id: <20170503203604.31462-8-ehabkost@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

hw/i386/kvm/clock.c

@@ -286,11 +286,6 @@ static void kvmclock_class_init(ObjectClass *klass, void *data)
     dc->realize = kvmclock_realize;
     dc->vmsd = &kvmclock_vmsd;
     dc->props = kvmclock_properties;
-    /*
-     * FIXME: Set only because we are not sure yet if this device
-     * will be outside the q35 sysbus whitelist.
-     */
-    dc->user_creatable = true;
 }
 
 static const TypeInfo kvmclock_info = {