package/qt5/qt5base: convert to qmake infrastructure

package/qt5/qt5base: convert to qmake infrastructure

Convert build, staging and target install to the qmake infra commands.
This removes a lot of conditional code because we solely rely on all install
rules being properly generated according to the configured options.

Of course we keep the configure command/logic as is, because qmake does not
yet exist.

Handling of the custom qt.conf is now done in the post staging hook.

Signed-off-by: Andreas Naumann <anaumann@ultratronik.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>