Instead of upgrading both kernels, allow support for selecting the
partition during sysupgrade.
Copy/Paste of Linux MX devices on the same target.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/22594
Signed-off-by: Robert Marko <robimarko@gmail.com>