Integrate meta-seco-intel/nspa/grub-bootscript

Commit: clea-os/layers/seco/meta-seco-intel@6edbaf07

[GRUB] Adapt GRUB env. and wic partition not assigning a fixed PARTUUID

Remove GRUB environment's variable root_env_bootarg. Let GRUB's bootscript discover the correct root device.

Remove no-more-needed fixed PARTUUID for rootfs partition.

Signed-off-by: Nicola Sparnacci nicola.sparnacci@seco.com