configure: Drop AIX host support

Nobody has mentioned AIX host support on the mailing list for years,
and we have no test systems for it so it is most likely broken.
We've advertised in configure for two releases now that we plan
to drop support for this host OS, and have had no complaints.
Drop the AIX host support code.

We can also drop the now-unused AIX version of sys_cache_info().

Note that the _CALL_AIX define used in the PPC tcg backend is
also used for Linux PPC64, and so that code should not be removed.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1504545540-8002-1-git-send-email-peter.maydell@linaro.org