add mcu flash size detect and auto config usart

Src/syscalls.c

@@ -16,6 +16,7 @@
 #include <unistd.h>
 #include <sys/wait.h>
 #include "gd32e23x_usart.h"
+#include "board_config.h"
 
 #undef errno
 extern int errno;
@@ -164,7 +165,7 @@ int _execve(char *name, char **argv, char **env)
 // USART0 printf重定向实现
 int __io_putchar(int ch) {
     // 等待发送缓冲区空
-    while (usart_flag_get(USART0, USART_FLAG_TBE) == RESET) {}
-    usart_data_transmit(USART0, (uint8_t)ch);
+    while (usart_flag_get(RS485_PHY, USART_FLAG_TBE) == RESET) {}
+    usart_data_transmit(RS485_PHY, (uint8_t)ch);
     return ch;
 }