A32/Thumb: Correct behaviour for UDF and Unpredictable instructions

Raise an exception instead of calling the interpreter and ASSERT-ing respectively.

src/frontend/A32/translate/impl/thumb16.cpp

@@ -885,7 +885,7 @@ bool ThumbTranslatorVisitor::thumb16_CBZ_CBNZ(bool nonzero, Imm<1> i, Imm<5> imm
 }
 
 bool ThumbTranslatorVisitor::thumb16_UDF() {
-    return InterpretThisInstruction();
+    return UndefinedInstruction();
 }
 
 // BX <Rm>