trivial: dell: show reasons for lack of updates in `UpdateError`
trivial: dell: show reasons for lack of updates in `UpdateError`

```
└─XPS 13 7390 TPM 2.0:
      Device ID:           c56e9f77cfee65151bdef90310776f9d62827f5a
      Summary:             Platform TPM device
      Current version:     7.2.1.0
      Vendor:              Dell Inc.
      Update Error:        Updating disabled due to TPM owernship
      Flags:               internal|require-ac|registered
```

fwupd/fwupd,hughsie/fwupd,hughsie/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,fwupd/fwupd,hughsie/fwupd