Genesis: separate channel state from instrument

paves way for FM macros
with this change, extended channel 3 mode breaks! do not use
until I diagnose the problem.

src/engine/platform/fmshared_OPN.h

@@ -0,0 +1,16 @@
+#ifndef _FMSHARED_OPN_H
+#define _FMSHARED_OPN_H
+
+#define ADDR_MULT_DT 0x30
+#define ADDR_TL 0x40
+#define ADDR_RS_AR 0x50
+#define ADDR_AM_DR 0x60
+#define ADDR_DT2_D2R 0x70
+#define ADDR_SL_RR 0x80
+#define ADDR_SSG 0x90
+#define ADDR_FREQ 0xa0
+#define ADDR_FREQH 0xa4
+#define ADDR_FB_ALG 0xb0
+#define ADDR_LRAF 0xb4
+
+#endif