kconfig check: remove --kconfig-check-{name} args

Prepare to move the kconfigcheck config into pmaports, so it can be
different per branch and so we can adjust it at the same time as
adjusting the kernel configs.

Once it is moved, pmbootstrap will not know the cateogry names in
advance anymore, so remove the logic for having category-specific
argument names.

In a future patch, we could add an option to manually override the
categories to be tested with one specific category (taking a string
argument), if there is demand for that.