Integrate meta-seconorth-distro/add_bootselect_env

Commit: seco-ne/yocto/layers/meta-seconorth-distro@48a866d7

seconorth:bootselect: Add environment mode for U-Boot

Get/Set the bootmode from the U-Boot environment instead of the RTC.

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Commit: seco-ne/yocto/layers/meta-seconorth-distro@d1a36f00

recipes:seco:bootselect: Add libubootenv as dependency