M263: Force enum PinName to 32-bit

NU_PINNAME_BIND(...) requires enum PinName to be 32-bit to encode module
binding information in it.

Author: ccli8

targets/TARGET_NUVOTON/TARGET_M261/PinNames.h

@@ -135,6 +135,9 @@ typedef enum {
     BUTTON1 = SW2,
     BUTTON2 = SW3,
 
+    // Force PinName to 32-bit required by NU_PINNAME_BIND(...)
+    FORCE_ENUM_PINNAME_32BIT = 0x7FFFFFFF,
+
 } PinName;
 
 #ifdef __cplusplus