cmd_part: fix typo in part command help text

All the sub-commands start with the main command anme, but it was
missing from one of the help texts.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
disk: support devices with HW partitions

Some device types (e.g. eMMC) have hardware-level partitions (for eMMC,
separate boot and user data partitions). This change allows the user to
specify the HW partition they wish to access when passing a device ID to
U-Boot Commands such as part, ls, load, ums, etc.

The syntax allows an optional ".$hwpartid" to be appended to the device
name string for those commands.

Existing syntax, for MMC device 0, default HW partition ID, SW partition
ID 1:

ls mmc 0:1 /

New syntax, for MMC device 0, HW partition ID 1 (boot0), SW partition
ID 2:

ls mmc 0.1:2 /

For my purposes, this is most useful for the ums (USB mass storage
gadget) command, but there's no reason not to allow the new syntax
globally.

This patch adds the core support infra-structure. The next patch will
provide the implementation for MMC.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
mmc: provide a select_hwpart implementation for get_device()

This enables specifying which eMMC HW partition to target for any U-Boot
command that uses the generic get_partition() function to parse its
command-line arguments.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
---
v2: Propagate error code from mmc_switch_part() rather than squashing it
    to -1 in mmc_select_hwpart().
cmd_mmc: use new mmc_select_hwpart() function

The implementation of mmc_select_hwpart() was cribbed from do_mmcops().
Update do_mmcops() to call mmc_select_hwpart() to avoid duplication.

Signed-off-by: Stephen Warren <swarren@nvidia.com>