part: Support getting whole disk from part_get_info_by_dev_and_name_or_num

This adds an option to part_get_info_by_dev_and_name_or_num to allow
callers to specify whether whole-disk partitions are fine.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Simon Glass <sjg@chromium.org>