tinyprintf: Add vprintf implementation

vprintf is used by panic() which is used in various SPL paths on some
boards.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Ian Campbell <ijc@hellion.org.uk>
Reviewed-by: Simon Glass <sjg@chromium.org>

lib/tiny-printf.c

@@ -130,6 +130,11 @@ abort:
 	return 0;
 }
 
+int vprintf(const char *fmt, va_list va)
+{
+	return _vprintf(fmt, va, putc);
+}
+
 int printf(const char *fmt, ...)
 {
 	va_list va;