kconfig: Turn pointless 'menuconfig's into 'config's

Same deal as in commit 677f1e6d ("config: Turn pointless/confusing
'menuconfig's into 'config's"), for a newly-introduced stuff.

Also clean up headers to be consistent with recent cleanups.

Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>