arrow-db410c: move from testing to community

arrow-db410c is a very recent device port, but it's almost fully working. Only missing thing is GPS. In theory it should work quite easily: I tested it yesterday but wasn't able to get a GPS fix. Reportedly the inbuilt GPS antenna of the DB410c is almost unusable so this is likely the problem. An external GPS antenna can be soldered but this is quite some work. (And I don't have one...)

I want to use my arrow-db410c to test the stable branch a bit. I'm planning to use it as a remote UART adapter (I connect UART to it and it exposes it via WiFi). For that it's nice if I don't need to install tons of updates all the time. I don't have much use for the stable branch during development otherwise. :)

PS: I realize postmarketOS wasn't made for SBCs. But the DB410c has Android Fastboot and other things that make it behave much like ordinary phones/tablets we support, so I think using postmarketOS on it works quite well. :)