USB STM32: fix header inclusion, removing mbed.h'

Fixes #13667 issue

Author: 0xc0170

targets/TARGET_STM/USBPhyHw.h

@@ -18,7 +18,13 @@
 #ifndef USBPHYHW_H
 #define USBPHYHW_H
 
-#include "mbed.h"
+#include <string.h>
+
+#include "platform/mbed_toolchain.h"
+#include "platform/mbed_error.h"
+#include "platform/mbed_assert.h"
+#include "platform/mbed_wait_api.h"
+#include "platform/mbed_power_mgmt.h"
 #include "USBPhy.h"
 #include "PeripheralPins.h"