doc: board: toradex: minor documentation update

- Update SPDX-License-Identifier from obsolete GPL-2.0+ to
  GPL-2.0-or-later.
- Add links to product websites of SoM and carrier board where missing.
- Add information about update U-Boot wrapper where missing.
- Add sectionauthor where missing.
- Update information about imx-seco from version 3.7.4 to 3.8.1.
- Various minor grammatic and spelling fixes.
- Improve whitespace by adding or removing new lines.
- Change from code-block for output to just Output::.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>