nitrogen6x: add Nitrogen6QP_MAX and SOMv2 support

BoundaryDevices' kernel has support for these boards, but their
machine config has not enabled them until in krogoth branch.

Change-Id: I31d93e2f3136ed647d673d29f64c20d7bb47af49
Task-number: QTBUG-56112
Reviewed-by: Rainer Keller <Rainer.Keller@qt.io>
Reviewed-by: Teemu Holappa <teemu.holappa@theqtcompany.com>