greybus: manifest: Remove vendor, product and unique-id from interface descriptor

These should come from control protocol instead.

For now, initialize this statically with a FIXME to not forget it later.

Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>