net: dsa: felix: configure the in-band autoneg property based on OF node info

Instead of trying to guess which operating modes need in-band
negotiation to be active and which ones don't, parse the available
information from the device tree. That will be correct in the cases we
can already guess, and more.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>