NUVOTON: Serial: Fix undeclared function gpio_set

ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]

Author: ccli8

targets/TARGET_NUVOTON/TARGET_M251/serial_api.c

@@ -24,6 +24,7 @@
 #include "mbed_error.h"
 #include "mbed_assert.h"
 #include "PeripheralPins.h"
+#include "gpio_api.h"
 #include "nu_modutil.h"
 #include "nu_bitutil.h"
 #include <string.h>

targets/TARGET_NUVOTON/TARGET_M261/serial_api.c

@@ -23,6 +23,7 @@
 #include "mbed_error.h"
 #include "mbed_assert.h"
 #include "PeripheralPins.h"
+#include "gpio_api.h"
 #include "nu_modutil.h"
 #include "nu_bitutil.h"
 #include <string.h>

targets/TARGET_NUVOTON/TARGET_M451/serial_api.c

@@ -22,6 +22,7 @@
 #include "mbed_error.h"
 #include "mbed_assert.h"
 #include "PeripheralPins.h"
+#include "gpio_api.h"
 #include "nu_modutil.h"
 #include "nu_bitutil.h"
 #include <string.h>

targets/TARGET_NUVOTON/TARGET_NANO100/serial_api.c

@@ -22,6 +22,7 @@
 #include "mbed_error.h"
 #include "mbed_assert.h"
 #include "PeripheralPins.h"
+#include "gpio_api.h"
 #include "nu_modutil.h"
 #include "nu_bitutil.h"
 #include <string.h>

targets/TARGET_NUVOTON/TARGET_NUC472/serial_api.c

@@ -22,6 +22,7 @@
 #include "mbed_error.h"
 #include "mbed_assert.h"
 #include "PeripheralPins.h"
+#include "gpio_api.h"
 #include "nu_modutil.h"
 #include "nu_bitutil.h"
 #include <string.h>