Unfortunately it turns out that libseccomp 2.2 still does not work
correctly on non-x86 architectures; return to the previous configure
setup of insisting on libseccomp 2.1 or better and i386/x86_64 and
disabling seccomp support in all other situations.

This reverts the two commits:
 * "seccomp: libseccomp version varying according to arch"
   (commit 896848f0)
 * "seccomp: update libseccomp version and remove arch restriction"
   (commit 8e27fc20)
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1428670681-23032-1-git-send-email-peter.maydell@linaro.org