Buttons: Change return value of board_buttons() and the type of btn_buttonset_t to uint32_t so that more than 8 buttons can be supported.

configs/cloudctrl/src/stm32_buttons.c

@@ -104,9 +104,9 @@ void board_button_initialize(void)
  * Name: board_buttons
  ****************************************************************************/
 
-uint8_t board_buttons(void)
+uint32_t board_buttons(void)
 {
-  uint8_t ret = 0;
+  uint32_t ret = 0;
   int i;
 
   /* Check that state of each key */