initial support for Mega65 extra ROM

c64/basic/rom_revision/a004.identifier.s

@@ -1,6 +1,10 @@
-// Compute's Mapping the 64, p89
+#if ROM_LAYOUT_STD || (ROM_LAYOUT_M65 && SEGMENT_BASIC_0)
+
+// Computes Mapping the 64, p89
 // 8 character name
 // MEGABAS2 = "MEGA BASIC 2"
 
 	.byte $4D,$45,$47,$41,$42,$41,$53,$32
 
+
+#endif // ROM layout