greybus: record type in operation structure

I've gone back and forth on this, but now that I'm looking at
asynchronous operations I know that the asynchronous callback will
want to know what type of operation it is handling, and right now
that's only available in the message header.

So record an operation's type in the operation structure, and use
it in a few spots where the header type was being used previously.
Pass the type to gb_operation_create_incoming() so it can fill
it in after the operation has been created.

Clean up the crap comments above the definition of the operation
structure.

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