Integrate meta-seconorth-machine/rauc-prep-1

Commit: seco-ne/yocto/layers/meta-seconorth-machine@20c8370e

bootscript: add rauc.slot=A to kernel command line

As a preparation for rauc, add initial slot variable. Rauc takes RAUC_CURRENT_BOOTNAME from kernel command line.

Signed-off-by: Mikhail Vanyulin mikhail.vanyulin@rtsoft.de