Add simple test app for I2S loopback (no USB)

examples/app_i2s_loopback_xvf3510/xua_conf.h

@@ -0,0 +1,37 @@
+
+#define NUM_USB_CHAN_OUT 2
+#define NUM_USB_CHAN_IN 2
+#define I2S_CHANS_DAC 2
+#define I2S_CHANS_ADC 2
+#define MCLK_441 (512 * 44100)
+#define MCLK_48 (512 * 48000)
+#define FREQ 48000
+#define MIN_FREQ FREQ
+#define MAX_FREQ FREQ
+
+#define EXCLUDE_USB_AUDIO_MAIN
+#define NUM_PDM_MICS 0
+#define XUD_TILE 1
+#define AUDIO_IO_TILE 0
+#define MIXER 0
+#define XUA_USB_EN 0
+
+#define SPDIF_TX_INDEX 0
+#define VENDOR_STR "XMOS"
+#define VENDOR_ID 0x20B1
+#define PRODUCT_STR_A2 "XUA Example"
+#define PRODUCT_STR_A1 "XUA Example"
+#define PID_AUDIO_1 1
+#define PID_AUDIO_2 2
+#define AUDIO_CLASS 2
+#define AUDIO_CLASS_FALLBACK 0
+#define BCD_DEVICE 0x1234
+#define XUA_DFU_EN 0
+
+#define N_BITS_I2S 32
+#define AUD_TO_USB_RATIO 1
+#define CODEC_MASTER 0
+
+
+/* TODO */
+#define XUA_DFU XUA_DFU_EN