D27601: KConfig: Convert to SPDX license statements

[Andreas Cord-Landwehr]

cordlandwehr added a task: T11550: Add SPDX License markers.

REPOSITORY
  R237 KConfig

REVISION DETAIL
  https://phabricator.kde.org/D27601

To: cordlandwehr
Cc: kde-frameworks-devel, LeGast00n, cblack, GB_2, michaelh, ngraham, bruns