net: dsa: qca8k: Add support for force mode for fixed link topology

net: dsa: qca8k: Add support for force mode for fixed link topology

A fixed link topology is commonly used to connect this switch (on port
0 or 6) to a SoC's MAC over SGMII. When inband negotiation is not used,
the switch needs to be configured to operate in force mode. As such,
enable support for force mode.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: George Moussalem <george.moussalem@outlook.com>
Link: https://patch.msgid.link/20260605-qca8337-force-mode-v2-1-d9a6b6545bfa@outlook.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>