pine64-pinephone: add myself as maintainer

I daily drive the pinephone. Adding myself to maintainers.

@MartijnBraam said he's also still daily driving it.

@z3ntu, @PureTryOut, @craftyguy, @dylanvanassche: depending on how much you use it, do you want to drop maintainership? Marking as draft until you responded, so we don't need another MR to change the maintainer lines.