greybus: send buffers without gbufs

Change the method that sends messages so that it sends "raw" buffers
rather than gbufs.  To do this, we supply the host device and
destination CPort when sending.  As with other recent patches,
change the name of the method to reflect that we're no longer
dealing with gbufs.

The interface has changed as well.  Now this routine will return a
"cookie" value.  The cookie is used to represent the outgoing
request, and is supplied by the caller if necessary to cancel a
previously-sent buffer.  We'll store the result in gbuf->hcd_data
for now (which produces the same result as before...).

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