Fix nrf52 USB (don't call delay() in loop() if connected via usb)

src/nrf52/main-nrf52.cpp

@@ -19,6 +19,10 @@ static inline void debugger_break(void)
                    "mov pc, lr\n\t");
 }
 
+bool loopCanSleep() {
+    return !tud_cdc_connected();
+}
+
 // handle standard gcc assert failures
 void __attribute__((noreturn)) __assert_func(const char *file, int line, const char *func, const char *failedexpr)
 {