doc: efm32: tag USB files for doxygen generation

lib/usb/usb_efm32.c

@@ -1,3 +1,9 @@
+/** @addtogroup usb_file USB peripheral API
+ * @ingroup peripheral_apis
+ *
+ * @sa usb_defines
+ * @copyright See @ref lgpl_license
+ */
 /*
  * This file is part of the libopencm3 project.
  *
@@ -26,6 +32,8 @@
 #include <libopencm3/usb/usbd.h>
 #include "usb_private.h"
 
+/**@{*/
+
 /* Receive FIFO size in 32-bit words. */
 #define RX_FIFO_SIZE 256
 
@@ -424,3 +432,5 @@ const struct _usbd_driver efm32lg_usb_driver = {
 	.set_address_before_status = 1,
 	.rx_fifo_size = RX_FIFO_SIZE,
 };
+
+/**@}*/

lib/usb/usb_efm32hg.c

@@ -1,3 +1,13 @@
+/** @addtogroup usb_file USB peripheral API
+ * @ingroup peripheral_apis
+ *
+ * @brief USB Peripheral for Happy Gecko
+ *
+ * The Happy Gecko uses the "standard" usb_dwc_otg core.
+ *
+ * @sa usb_defines
+ * @copyright See @ref lgpl_license
+ */
 /*
  * This file is part of the libopencm3 project.
  *
@@ -28,6 +38,8 @@
 #include "usb_private.h"
 #include "usb_dwc_common.h"
 
+/**@{*/
+
 /* Receive FIFO size in 32-bit words. */
 #define RX_FIFO_SIZE 256
 
@@ -124,3 +136,5 @@ const struct _usbd_driver efm32hg_usb_driver = {
 	.set_address_before_status = 1,
 	.rx_fifo_size = RX_FIFO_SIZE,
 };
+
+/**@}*/