doc: board: phytec: phycore-am62x: Fix Link to Documentation

We moved our documentation to another hoster and therefore the URL
changed. Point to the latest documentation instead of release versions
to not link out-dated documentation.

Signed-off-by: Daniel Schultz <d.schultz@phytec.de>
Reviewed-by: Wadim Egorov <w.egorov@phytec.de>