pseudo: Add uninative configuration sanity check

When building pseudo-native to work with uninative, we need to ensure the
configuration will work on all supported target systems. This means
"new clone" semantics, xattr and statvfs support in particular. It is
extremely unlikely we'd run on a system without any of these but add
a check just to be sure when uninative is enabled.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit ea5b208e)
Signed-off-by: Steve Sakoman <steve@sakoman.com>