vsprintf.h is gPXE-specific; move it to include/gpxe

src/core/vsprintf.c

 #include <stdio.h>
 #include <console.h>
 #include <errno.h>
-#include <vsprintf.h>
+#include <gpxe/vsprintf.h>
 
 /** @file */
 

src/hci/mucurses/print.c

 #include <curses.h>
 #include <stdio.h>
 #include <stddef.h>
-#include <vsprintf.h>
+#include <gpxe/vsprintf.h>
 #include "mucurses.h"
 
 /** @file

src/include/vsprintf.h → src/include/gpxe/vsprintf.h

-#ifndef VSPRINTF_H
-#define VSPRINTF_H
+#ifndef _GPXE_VSPRINTF_H
+#define _GPXE_VSPRINTF_H
 
 /** @file
  *
 
 extern size_t vcprintf ( struct printf_context *ctx, const char *fmt,
 			 va_list args );
-#endif /* VSPRINTF_H */
+#endif /* _GPXE_VSPRINTF_H */