windeployqt: Add missing "audio" plugins for QtMultimedia.

Task-number: QTBUG-39157
Change-Id: I88055eed7b430c14e1d1e13bdeee558a63763d8d
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Exclude qtdiag when QtGui is not available.

Task-number: QTBUG-39118
Change-Id: I54f6879ef58e5b7b7bc2c20840524f4af5433921
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>