add usb audio, cdc, and midi stub files for doxy

- add stub files to relevant makefiles
- include <stdint.h> in respective headers to fix compilation

include/libopencm3/usb/audio.h

@@ -40,6 +40,8 @@ LGPL License Terms @ref lgpl_license
 #ifndef LIBOPENCM3_USB_AUDIO_H
 #define LIBOPENCM3_USB_AUDIO_H
 
+#include <stdint.h>
+
 /*
  * Definitions from the USB_AUDIO_ or usb_audio_ namespace come from:
  * "Universal Serial Bus Class Definitions for Audio Devices, Revision 1.0"

include/libopencm3/usb/cdc.h

@@ -38,6 +38,8 @@ LGPL License Terms @ref lgpl_license
 #ifndef __CDC_H
 #define __CDC_H
 
+#include <stdint.h>
+
 /* Definitions of Communications Device Class from
  * "Universal Serial Bus Class Definitions for Communications Devices
  * Revision 1.2"

include/libopencm3/usb/midi.h

@@ -38,6 +38,8 @@ LGPL License Terms @ref lgpl_license
 #ifndef LIBOPENCM3_USB_MIDI_H
 #define LIBOPENCM3_USB_MIDI_H
 
+#include <stdint.h>
+
 /*
  * Definitions from the USB_MIDI_ or usb_midi_ namespace come from:
  * "Universal Serial Bus Class Definitions for MIDI Devices, Revision 1.0"