target-openrisc: TYPE_OPENRISC_CPU should be abstract

A basic assumption of CPU subtypes is that only specific models get
instantiated. A user is not supposed to instantiate an <arch>-cpu.
Suppress it via abstract = true, which also drops or32-cpu from
-cpu ? output.

Cc: qemu-stable@nongnu.org
Cc: Jia Liu <proljc@gmail.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>

target-openrisc/cpu.c

@@ -159,7 +159,7 @@ static const TypeInfo openrisc_cpu_type_info = {
     .parent = TYPE_CPU,
     .instance_size = sizeof(OpenRISCCPU),
     .instance_init = openrisc_cpu_initfn,
-    .abstract = false,
+    .abstract = true,
     .class_size = sizeof(OpenRISCCPUClass),
     .class_init = openrisc_cpu_class_init,
 };