trace: move hw/mem/pc-dimm.c trace points into correct file

trace: move hw/mem/pc-dimm.c trace points into correct file

The trace points for hw/mem/pc-dimm.c were mistakenly put
in the hw/i386/trace-events file, instead of hw/mem/trace-events
in

  commit 5eb76e480b42206d3640c1aab8a376ba350f70bb
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Thu Jun 16 09:40:10 2016 +0100

    trace: split out trace events for hw/i386/ directory

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Message-id: 1473872624-23285-4-git-send-email-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>