M487: Support PinName enum override

User can override PinName enum in PinNames.h for custom targets. E.g.:

1.  Add into mbed_app.json:
    target.custom-pinname-file: "\"CustomPinName.h\"",
2.  Implement PinName enum in CustomPinName.h

Author: ccli8

targets/TARGET_NUVOTON/TARGET_M480/PinNames.h

@@ -70,6 +70,8 @@ typedef enum {
     PullDefault = PullUp
 } PinMode;
 
+#if !defined(MBED_CONF_TARGET_CUSTOM_PINNAME_FILE)
+
 typedef enum {
     // Not connected
     NC = (int)0xFFFFFFFF,
@@ -146,6 +148,12 @@ typedef enum {
 
 } PinName;
 
+#else
+
+#include MBED_CONF_TARGET_CUSTOM_PINNAME_FILE
+
+#endif
+
 #ifdef __cplusplus
 }
 #endif

targets/targets.json

@@ -12766,6 +12766,10 @@
                 "help": "Enable SPIM CCM mode to spare 32KiB SRAM for normal use",
                 "value": 0
             },
+            "custom-pinname-file": {
+                "help": "Header file to override PinName enum in PinNames.h",
+                "value": null
+            },
             "gpio-irq-debounce-enable": {
                 "help": "Enable GPIO IRQ debounce",
                 "value": 0