makefile: generate trace-events-all upfront

Files should not be created in the build dir during the
'make install' phase. List 'trace-events-all' as a
generated file so that it gets created upfront during
build.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Message-id: 20170228122901.24520-3-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>