initial support for Mega65 extra ROM

c64/kernal/memory/fe25.memtop.s

@@ -1,9 +1,10 @@
+#if ROM_LAYOUT_STD || (ROM_LAYOUT_M65 && SEGMENT_KERNAL_0)
 
 //
 // Official Kernal routine, described in:
 //
-// - [RG64] C64 Programmer's Reference Guide   - page 288
-// - [CM64] Compute's Mapping the Commodore 64 - page 240
+// - [RG64] C64 Programmers Reference Guide   - page 288
+// - [CM64] Computes Mapping the Commodore 64 - page 240
 //
 // CPU registers that has to be preserved (see [RG64]): .A
 //
@@ -23,3 +24,6 @@ memtop_set: // for compatibility reasons this has to start at $FE2D
 	stx MEMSIZK+0
 	
 	rts
+
+
+#endif // ROM layout