build system can create different ROMs per platforn

c64/basic/,platform_ultimate64/,aliases-ultimate64.s

@@ -0,0 +1,10 @@
+
+;; Registers according to Ultimate 64 Command Interface ddescription,
+;; https://1541u-documentation.readthedocs.io/en/latest/command%20interface.html
+
+	.alias U64_CONTROL           $DF1C ; write
+	.alias U64_STATUS            $DF1C ; read
+	.alias U64_COMMAND_DATA      $DF1D ; write
+	.alias U64_IDENTIFICATION    $DF1D ; read
+	.alias U64_RESPONSE_DATA     $DF1E ; read only
+	.alias U64_STATUS_DATA       $DF1F ; read only