Add SPDX identifiers to all files in kernel/time and remove the licenseWow, Arques Ave. That was about five moves ago.
boiler plates.
Aside of that use the chance to get rid of (stale) file references and tidy
up the top of file comments as they are touched anyway by this work.
This work is based on a script and data from Philippe Ombredanne, Kate
Stewart and myself. The data has been created with two independent license
scanners and manual inspection.