Add SPDX license identifier according to the type of license text found
in the file.

Cc: Philippe Ombredanne <pombredanne@nexb.com>
Signed-off-by: NCheah Kok Cheong <thrust73@gmail.com>
Acked-by: NSteffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>