Add `qcom-wip` device type to help supporting new devices

!31 (closed) was an attempt at creating a dummy device type in order to make it easier to support new devices. However, by trying to be completely generic, it was overly complex and consequently was never actually finished.

In the real world, devices likely to be supported are only qcom-based ones (at least for now), so we shouldn't bother with addressing non-existent use-cases and instead provide a simple-ish way of building images for new qcom devices.

This is achieved by providing a new qcom-wip device type, which does the following:

• use the generic qcom-support-common instead of <soc>-support
• install all .deb packages found under devices/qcom/packages
• copy any droid-juicer config file under devices/qcom/droid-juicer to the image

With those changes, building an image for a yet-unsupported device requires the following steps:

• build a .deb kernel package for this device (using make bindeb-pkg on a downstream tree, for example) and copy it to the devices/qcom/packages folder
• fill in the devices/qcom/configs/wip.json file with the appropriate information for the target device
• optional: create a droid-juicer config named <compatible>.toml and copy it to the devices/qcom/droid-juicer folder
• run ./build.sh -t qcom-wip