Added USB microphone example

examples/usb-microphone/arm7/source/usb_descriptors.h

@@ -0,0 +1,24 @@
+#pragma once
+
+enum
+{
+    STRID_LANGID = 0,
+    STRID_MANUFACTURER,
+    STRID_PRODUCT,
+    STRID_SERIAL,
+    STRID_AUDIO_INTERFACE
+};
+
+enum
+{
+    ITF_NUM_AUDIO_CONTROL = 0,
+    ITF_NUM_AUDIO_STREAMING,
+    ITF_NUM_TOTAL
+};
+
+#define UAC2_ENTITY_MIC_INPUT_TERMINAL  0x01
+#define UAC2_ENTITY_FEATURE_UNIT        0x02
+#define UAC2_ENTITY_MIC_OUTPUT_TERMINAL 0x03
+#define UAC2_ENTITY_CLOCK               0x04
+
+#define EPNUM_AUDIO_IN      0x81