Add Raspberry Pi 5 support

Spotted recently: initial DTB support landed in v6.12-rc1 (see https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=faa3381267d01a389b13038504079c85c0bc4392).

I haven't looked into that yet, but it would be nice to start thinking about building an image for it.