qt5: use the new base bbclass to get qt.conf generated

populate_sdk_qt5 was split into two bbclasses and the qt.conf
generation we need is in the new base class.

Change-Id: I7fe2f3bdc0bf88e795add996f58b592ea12aa8a3
Reviewed-by: aavit <eirik.aavitsland@theqtcompany.com>