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/filetests/filetests/isa/aarch64/heap_addr.clif

@@ -26,7 +26,7 @@ block0(v0: i64, v1: i32):
 ;   csel x0, x14, x13, hi
 ;   ret
 ; block2:
-;   udf
+;   udf #0xc11f
 
 function %static_heap_check(i64 vmctx, i32) -> i64 {
     gv0 = vmctx
@@ -48,5 +48,5 @@ block0(v0: i64, v1: i32):
 ;   csel x0, x11, x10, hi
 ;   ret
 ; block2:
-;   udf
+;   udf #0xc11f
 

cranelift/filetests/filetests/isa/aarch64/traps.clif

@@ -8,7 +8,7 @@ block0:
 }
 
 ; block0:
-;   udf
+;   udf #0xc11f
 
 function %g(i64) {
 block0(v0: i64):