fairphone-fp4: new device (Fairphone 4)

Day 1 support in postmarketOS 😉

https://wiki.postmarketos.org/wiki/Fairphone_4_(fairphone-fp4)

Currently just relatively limited support with (close to) mainline kernel: simple-framebuffer screen, buttons, USB. Hopefully new hardware support will be coming soon, similar SoCs have a relatively good feature set (but not sdm845 standards yet).

Downstream kernel sources aren't released yet so that will come later.