Cranelift AArch64: Use an allocated encoding for Udf (#4281)

Preserve the current behaviour when code is generated for SpiderMonkey.

Copyright (c) 2022, Arm Limited.

cranelift/codegen/src/machinst/buffer.rs

@@ -1672,6 +1672,7 @@ mod test {
 
         buf.bind_label(label(1));
         let inst = Inst::Udf {
+            use_allocated_encoding: true,
             trap_code: TrapCode::Interrupt,
         };
         inst.emit(&[], &mut buf, &info, &mut state);