st24: move decode state to header file

src/lib/rc/st24.h

@@ -55,6 +55,15 @@ enum ST24_PACKET_TYPE {
 	ST24_PACKET_TYPE_TRANSMITTERGPSDATA
 };
 
+enum ST24_DECODE_STATE {
+	ST24_DECODE_STATE_UNSYNCED = 0,
+	ST24_DECODE_STATE_GOT_STX1,
+	ST24_DECODE_STATE_GOT_STX2,
+	ST24_DECODE_STATE_GOT_LEN,
+	ST24_DECODE_STATE_GOT_TYPE,
+	ST24_DECODE_STATE_GOT_DATA
+};
+
 #pragma pack(push, 1)
 typedef struct {
 	uint8_t	header1;			///< 0x55 for a valid packet