trace: add build framework for merging trace-events files

Switch make rules over to use trace-events-all as the
master trace events input file. Add rule that will
construct trace-events-all from $(trace-events-y).

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 1466066426-16657-2-git-send-email-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>