uboot-imx

disk: part: scan the disk if the part_type is unknown

If a DUT do not have partition table, and we write one with 'gpt write'
cmd, we should able to list the partition with 'part list' cmd.
It's reasonable to scan the disk again if the initial part_type is
unknown in case we just write a new one into disk.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>