Update the kernel to 5.10.104. This should pull the latest security
fixes, i.e. for CVE-2022-0847.

With this it seems to be necessary to disable
CONFIG_STACKPROTECTOR_PER_TASK to build it inside Yocto dunfell.
It seems to be a problem of missing headers inside gcc-plugin.

Remove the PREFERRED kernel variables from imx6ull, that are derived
from guf.inc.

BCS 746-000735