* Linux: Update kernel 5.15.25
Use highest available kernel version in Buildroot 2021.08 (5.13)
* Update Hardkernel patches to Linux 5.15
* Update generic-x86-64/ova kernel config/patches for 5.15
* Drop Intel e1000e Sourceforge driver
The driver has been discontinued sometime last year. The main reason the
out-of-tree kernel has been enabled was for support for the i219-V
network chips which meanwhile are supported in mainline.
* Fix migration from Barebox GRUB
Create GRUB env which defaults to the boot slot we are updating to. This
makes sure that the newly installed OS version will be booted on next
reboot even if installed on boot slot B.
* Remove duplicate config.txt copy statement
* Use static cmdline.txt file
Instead of dynamically creating cmdline.txt use a static version of it.
This aligns with other boot loader/firmware configuration files and makes
it easier to customize the file per board.
* Rename Intel NUC machine to Generic x86-64
The Intel NUC machine has evolved and supports various x86-64 machines
today. Rename the board.
Note that this does not address the migration issue. This will be
handled separately.
* Update Scripts/Documentation
