kernel config: tidy up config fragments

[foersleo]

There is some things to tidy up for the parts we set for our kernel configs:

• [x] Usage of CONFIG_FOO=n instead of # CONFIG_FOO is not set to deactivate a setting
• [ ] Check if there is any conflicts that merge-config brings up (e.g. intended to have something build in, but dependency options are build as module; merge-config will complain about those)