move wic files to files/wic/

This is now the only expected path for wic files.

Since oe-core commit 07e41060 ("sanity: Add check for old wks/wic
paths"), the previously supported paths throw an error like:

    wic/wks files at [..]/meta-rauc-community/meta-rauc-community/meta-rauc-beaglebone/wic need to be moved to files/wic within the layer to be found/used

Signed-off-by: Enrico Jörns <ejo@pengutronix.de>

Author: ejoerns