dt-bindings: net: Document QCA808x PHYs

Add Documentation for QCA808x PHYs for the additional LED configuration
for this PHY.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20240125203702.4552-5-ansuelsmth@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>