MT#61856 media_player: move `KERNEL_IDX_NONE` to header

Make this sentinel visible via header, because anywhere
where the `kernel_idx` is declared/used,
this won't be usable due to limited visibility to .c file.

Change-Id: I159fe1a87e92656fdd790dd98569cfebe80d4ddd

daemon/media_player.c

@@ -27,7 +27,6 @@
 #include "arena.h"
 
 #define DEFAULT_AVIO_BUFSIZE 4096
-#define KERNEL_IDX_NONE UINT_MAX
 
 typedef enum {
 	MPC_OK = 0,

include/media_player.h

@@ -17,6 +17,7 @@ struct packet_stream;
 struct codec_packet;
 struct media_player;
 
+#define KERNEL_IDX_NONE UINT_MAX
 
 typedef struct {
 	long long start_pos;