Dynamic selection of i.MX8MM U-Boot environment config in Linux userspace

This MR solves https://git.kontron-electronics.de/sw/ked/plan/plan-yocto/-/issues/1244 by:

1. Updating libubootenv to v0.3.4
2. Extending libubootenv to support namespace autoselection via DT (upstream pending: http://patchwork.ozlabs.org/project/swupdate/cover/20230816095641.149618-1-frieder@fris.de/)
3. Updating U-Boot to export current environment device via DT

It also changes the location of the environment in the eMMC HW partition (boot0) to be at the end of the partition.

Tested on a BL i.MX8MM (using SPI NOR and SD card) and BL OSM-S i.MX8MM Rev 0 (using eMMC Boot).

CC: @estoll @mwalle