wil6210: add SPDX license identifiers

Change all files to add SPDX license identifiers and
remove license text.
This is only an administrative change, there is no change
in actual license or copyright for any file.

Signed-off-by: Lior David <liord@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>