[USB] Disable USB pullup hack when internal pullups are available

Previously, when no external pullup control was available, the core
would apply a hack to override an external fixed pullup. However, on
chips that have internal pullups, these will be automatically
controlled, so this is not needed at all.

This probably needs to be more configurable by board, but this is enough
to for the specific board we are working with now.

See stm32duino#885

Author: matthijskooijman

cores/arduino/stm32/usb/usbd_if.c

@@ -18,6 +18,9 @@
 
 WEAK void USBD_reenumerate(void)
 {
+// If SDIS (soft disconnect) is enabled, assume there are internal
+// pullups which will be managed automatically, so do nothing.
+#ifndef USB_OTG_DCTL_SDIS
 #ifndef USBD_REENUM_DISABLED
   /* Re-enumerate the USB */
 #ifdef USB_DISC_PIN
@@ -38,6 +41,7 @@ WEAK void USBD_reenumerate(void)
   /*delay(USBD_ENUM_DELAY);*/
 #endif /* USB_DISC_PIN */
 #endif /* USBD_REENUM_DISABLED */
+#endif /* USB_OTG_DCTL_SDIS */
 }
 
 #ifdef USBD_USE_CDC