Integrate meta-seconorth-mtk/fix_boot_scr

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Commit: seco-ne/yocto/layers/meta-seconorth-mtk@24808427

uboot:scripts: Change slot names to match bootselect names

Historically, we use the names "alternative", "regular" and "regularB"
to name the three operating systems on the boards. The bootselect tool
also sets these names in the U-Boot ENV. Change the boot script to align
with these names, too.