device-qemu-amd64-xfce4.post-install

For testing changes for device categorization, it is useful to have
a device in each of the categories. The PinePhone is close to being
moved to main/, but it doesn't fulfill all requirements yet.

The QEMU "device ports" are very simple since QEMU currently only
emulates a rather limited set of hardware features. All available features
are working correctly (especially after the recent rework of the QEMU
packages). I suppose it is also usable as a "daily driver", at least for
its intended purpose (a virtual machine for testing postmarketOS changes). :)

Given that everyone can run QEMU, everyone could potentially maintain
it. For now I have added myself as maintainer since I did most of the
recent cleanup. Add drebrez as second maintainer.

Overall it seems useful to have qemu-* in main/, especially because
it is now the device that is selected by default in pmbootstrap.