main/linux-postmarketos-stericsson: upgrade to 5.15-rc1 + add myself as maintainer + support anbox kconfig

eMMC hang fix patch needs rebasing on 5.15-rc1. I am aware the defconfig hasn't been updated as well.

Rebase done. I'm not sure if my changes are correct as I'm not familiar with the eMMC subsystem, but it works for me on skomer and I don't notice any regressions. Someone more experienced is very welcome to review it (emmc.patch).

Also enabled the NTFS3 driver for fun.

WIP because I want to verify that Waydroid works with this setup. Seems to work. I ran into some permission denied thing, but I don't feel like spending more time on this right now. Either way, no missing kernel modules any more.