target: improve error messaging in `target create`

target: improve error messaging in `target create`

There are a couple of issues with the usage string for `target create`,
namely:
* `-chain-position` is allowed to be not the first option.
* `-chain-position` should be ommited alltogether on ARM targets when
  DAP is specified.

Before the patch:
```
> openocd -c 'target create name testee'
...
  target create name type '-chain-position' name [options ...]
```

After the patch:
```
> openocd -c 'target create name testee'
...
-chain-position ?name? required when creating target
> openocd -c 'target create'
...
  target create name type [options ...]
```

Change-Id: Ia21a99ce6a4086e2e0676f5ef4685da3514a4f69
Signed-off-by: Evgeniy Naydanov <evgeniy.naydanov@syntacore.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8860
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins