More small pieces of ESS emulation

src/include/86box/snd_sb_dsp.h

@@ -141,6 +141,7 @@ typedef struct sb_dsp_t {
     uint8_t azt_eeprom[AZTECH_EEPROM_SIZE]; /* the eeprom in the Aztech cards is attached to the DSP */
 
     uint8_t ess_regs[256]; /* ESS registers. */
+    uint8_t ess_playback_mode;
 
     mpu_t *mpu;
 } sb_dsp_t;