When using pmbootstrap, you usually select the device you want to work
on using 'pmbootstrap init', generate the rootfs and can then run more
commands in the context of the device.
The same needs to be done before using QEMU (to generate the rootfs).
But for some reason 'pmbootstrap qemu' requires setting the --arch
parameter when running QEMU for a foreign architecture, even when the
device is still selected in pmbootstrap.
Even more confusing is that setting "--arch arm" always selects
device-qemu-vexpress, but this is not immediately clear from the name.
Let's make this a lot more intuitive by making sure there is a QEMU
device selected when running 'pmbootstrap qemu'. We can then use the
device information to infer the architecture automatically.
f536fd9cb9