clarify PicoDrive's license

- PicoDrive was originally released by fDave with simple
  "free for non-commercial use / For commercial use, separate licencing
  terms must be obtained" license and I kept it in my releases.
- in 2011, fDave re-released his code (same that I used as base
  many years ago) dual licensed with GPLv2 and MAME licenses:
    https://code.google.com/p/cyclone68000/

Based on the above I now proclaim that the whole source code is licensed
under the MAME license as more elaborate form of "for non-commercial use".
If that raises any doubt, I announce that all my modifications (which
is the vast majority of code by now) is licensed under the MAME license,
as it reads in COPYING file in this commit.

This does not affect ym2612.c/sn76496.c that were MAME licensed already
from the beginning.

cpu/drc/cmn.c

@@ -1,3 +1,10 @@
+/*
+ * PicoDrive
+ * Copyright (C) 2009,2010 notaz
+ *
+ * This work is licensed under the terms of MAME license.
+ * See COPYING file in the top-level directory.
+ */
 #include <stdio.h>
 #ifdef __linux__
 #include <sys/mman.h>

cpu/drc/emit_arm.c

@@ -1,8 +1,10 @@
-// Basic macros to emit ARM instructions and some utils
-
-// (c) Copyright 2008-2009, Grazvydas "notaz" Ignotas
-// Free for non-commercial use.
-
+/*
+ * Basic macros to emit ARM instructions and some utils
+ * Copyright (C) 2008,2009,2010 notaz
+ *
+ * This work is licensed under the terms of MAME license.
+ * See COPYING file in the top-level directory.
+ */
 #define CONTEXT_REG 11
 
 // XXX: tcache_ptr type for SVP and SH2 compilers differs..

cpu/drc/emit_x86.c

@@ -1,4 +1,10 @@
 /*
+ * Basic macros to emit x86 instructions and some utils
+ * Copyright (C) 2008,2009,2010 notaz
+ *
+ * This work is licensed under the terms of MAME license.
+ * See COPYING file in the top-level directory.
+ *
  * note:
  *  temp registers must be eax-edx due to use of SETcc and r/w 8/16.
  * note about silly things like emith_eor_r_r_r: