Added 5.4.0 change file.

Change-Id: I623b42d5f4f565ee7cf2d064e52609a99636bd6a
Reviewed-by: Jani Heikkinen <jani.heikkinen@theqtcompany.com>
Merge remote-tracking branch 'origin/5.4.0' into 5.4

Change-Id: Ice62a75ba6ff094e22e8affbecf26f4d3bf2f282