initial support for Mega65 extra ROM

c64/kernal/iostack/f4a5.load.s

@@ -1,8 +1,10 @@
+#if ROM_LAYOUT_STD || (ROM_LAYOUT_M65 && SEGMENT_KERNAL_0)
+
 //
 // Official Kernal routine, described in:
 //
-// - [RG64] C64 Programmer's Reference Guide   - page 286
-// - [CM64] Compute's Mapping the Commodore 64 - page 231
+// - [RG64] C64 Programmers Reference Guide   - page 286
+// - [CM64] Computes Mapping the Commodore 64 - page 231
 // - IEC reference at http://www.zimmers.net/anonftp/pub/cbm/programming/serial-bus.pdf
 //
 // CPU registers that has to be preserved (see [RG64]): none
@@ -55,3 +57,6 @@ LOAD:
 #endif
 
 	jmp lvs_illegal_device_number
+
+
+#endif // ROM layout