common/gnttab: Improve logging message by including relevent domid

common/gnttab: Improve logging message by including relevent domid

Several logging messages cite "bad ref %#x", without identifying which domain
the ref belongs to.  Add a domain back-pointer to struct grant_table to
improve the debugability.

While editing the messages, clean up some others:

 * Remove extranious punctuation
 * Use d%d rather than Dom%d
 * Remove "gnttab_transfer:" prefixes, as it is included by the gdprintk()
 * Reflow several messages to not be split across multiple lines

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Julien Grall <julien.grall@linaro.org>