oneplus-billie2: new device (OnePlus Nord N100)

So far the debug-shell in initfs works. The device uses dynamic partitions, so that has to be figured out to get a proper rootfs.

One thing to look out for is that mount_subpartitions task in initfs hangs, so pmos_boot=sth was added to kernel cmdline to skip it. This is also related to dynamic partitions, btw.