[WIP] bq Aquaris U (chaozu) support

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@JBBgameich or anyone else: if you have updated the code for another review, please open up a new merge request. Sorry for the trouble.

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The device and kernel package are currently build-tested only. I did not yet flash the images, but I'll do as soon as I can. I'll remove the WIP label as soon as it boots and I have SSH access. A code review would already be nice because I have no experience with APKGBUILDS yet. I started writing a wiki page here: Aquaris U (PostmarketOS Wiki)

EDIT: I can't test it on my device currently because after I tried to flash the latest Stock ROM using the official flash tool (which crashed the first time after always working great before), the phone only has a LittleKernel in locked state left on it. I'd need some OEM keys to install something on it again. Support is contacted, but that can take time I guess ...

EDIT 2: Got a OEM key from the support now, I'm going to recover the phone now

EDIT 3: It lives again :)