Added derivation of TDF base class, for AVR8 targets.

Includes initialisation and validation code.

build/scripts/TargetDescriptionFiles/Register.php

@@ -0,0 +1,9 @@
+<?php
+namespace Bloom\BuildScripts\TargetDescriptionFiles;
+
+class Register
+{
+    public ?string $name = null;
+    public ?int $offset = null;
+    public ?int $size = null;
+}