bluez: Update licencing and copyright headers

 • Add a file encoding header
 • Update the copyright to 2015
 • Add an SPDX license identifier header
 • Add missing GPL-2.0+ header on a couple of files

I have assumed that the files which were previously missing a licence
are under the same licence as the rest of the Python files here —
GPL-2.0+.

Signed-off-by: Philip Withnall <philip.withnall@collabora.co.uk>

Differential Revision: https://phabricator.apertis.org/D873