EHCI: fix xfer failed with disconnected device as stalled

- change CFG_TUH_ENDPOINT_MAX to 16 (max endpoint pair per device) if
not defined
- change QHD_MAX for EHCI, should be user configurable and more
optimized in the future

hw/bsp/imxrt/family.c

@@ -131,7 +131,10 @@ void board_init(void)
     freq = CLOCK_GetOscFreq() / (CLOCK_GetDiv(kCLOCK_UartDiv) + 1U);
   }
 
-  LPUART_Init(UART_PORT, &uart_config, freq);
+  if ( kStatus_Success != LPUART_Init(UART_PORT, &uart_config, freq) ) {
+    // failed to init uart, probably baudrate is not supported
+    // TU_BREAKPOINT();
+  }
 
   //------------- USB -------------//
   // Note: RT105x RT106x and later have dual USB controllers.