cpu/esp8266: Moved stdio_init before periph_init

- This guarantees that DEBUG() is available early in boot process
- Forgotten in https://github.com/RIOT-OS/RIOT/pull/11367, this fixes broken stdio

cpu/esp8266/startup.c

@@ -33,6 +33,7 @@
 #include "board.h"
 #include "common.h"
 #include "exceptions.h"
+#include "stdio_base.h"
 #include "syscalls.h"
 #include "tools.h"
 #include "thread_arch.h"
@@ -159,6 +160,9 @@ void system_init(void)
     extern void flash_drive_init (void);
     flash_drive_init();
 
+    /* initialize stdio*/
+    stdio_init();
+
     /* trigger static peripheral initialization */
     periph_init();
 
@@ -693,6 +697,9 @@ void __attribute__((noreturn)) IRAM cpu_user_start (void)
     extern void flash_drive_init (void);
     flash_drive_init();
 
+    /* initialize stdio*/
+    stdio_init();
+
     /* trigger static peripheral initialization */
     periph_init();