Define USBTX and USBRX for targets missing it

Define USBTX and USBRX for the LPC11U37H and the MTS_MDOT_F405RG.

targets/TARGET_NXP/TARGET_LPC11UXX/TARGET_LPC11U37H_401/PinNames.h

@@ -150,6 +150,10 @@ typedef enum {
 
     // Not connected
     NC = (int)0xFFFFFFFF,
+
+    // Standard but not supported pins
+    USBTX = NC,
+    USBRX = NC,
 } PinName;
 
 typedef enum {

targets/TARGET_STM/TARGET_STM32F4/TARGET_MTS_MDOT_F405RG/PinNames.h

@@ -140,7 +140,12 @@ typedef enum {
     USB_OTG_HS_ULPI_NXT = PC_3,
 
     // Not connected
-    NC = (int)0xFFFFFFFF
+    NC = (int)0xFFFFFFFF,
+
+    // Standard but not supported pins
+    USBTX = NC,
+    USBRX = NC
+
 } PinName;
 
 #ifdef __cplusplus