greybus: update a few header file comments

Add a GPLv2 tag and reword some comments at the top of "greybus_desc.h"
and "svc_msg.h".

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus: fix document version number

Two spots use the old "0.draft" version number for the Greybus
protocol specification.  We've updated that to be 0.1.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>