audit: define audit_is_compat in kernel internal header

We were exposing a function based on kernel config options to userspace.
This is wrong.  Move it to the audit internal header.

Suggested-by: Chris Metcalf <cmetcalf@tilera.com>
Signed-off-by: Eric Paris <eparis@redhat.com>

diff --cc include/linux/audit.h
Simple merge

diff --cc include/uapi/linux/audit.h
Simple merge