tools/nolibc/stdio: Implement vprintf()

vprintf() is equivalent to vfprintf() to stdout so implement it as a simple
wrapper for the existing vfprintf(), allowing us to build kselftest.h.

Suggested-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Willy Tarreau <w@1wt.eu>
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>