sdvx: Allow setting digital amp level from sdvxio

For SDVX 1-4: passes amp values through as-is

For SDVX5: ignores the amp volume control (as the game uses windows volume controls, which will work without any hooks)

src/main/bemanitools/sdvxio.h

@@ -98,4 +98,8 @@ uint16_t sdvx_io_get_input_gpio(uint8_t gpio_bank);
 
 uint16_t sdvx_io_get_spinner_pos(uint8_t spinner_no);
 
+/* Sets the volume of the digital amps if possible */
+
+bool sdvx_io_set_amp_volume(uint8_t primary, uint8_t headphone, uint8_t subwoofer);
+
 #endif