dt-bindings: net: sparx5: document RGMII delays

dt-bindings: net: sparx5: document RGMII delays

The lan969x switch device supports two RGMII port interfaces that can be
configured for MAC level rx and tx delays. Document two new properties
{rx,tx}-internal-delay-ps in the bindings, used to select these delays.

Tested-by: Robert Marko <robert.marko@sartura.hr>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Daniel Machon <daniel.machon@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20241220-sparx5-lan969x-switch-driver-4-v5-9-fa8ba5dff732@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>