disk: Provide API to get partition by name for specific type

There is already existing function part_get_info_by_name().
But sometimes user is particularly interested in looking for only
specific partition type. This patch implements such an API that
provides partition searching by name for specified partition type.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>