greybus: interface: Expose DDBL1 manufacturing and production id in sysfs

These ids are already fetched from the SVC, but were never exposed to
sysfs. Userspace may be interested in using these values and hence these
must be exposed to it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>