dt-bindings: net: ethernet-controller: Add internal delay properties

Internal Receive and Transmit Clock Delays are a common setting for
RGMII capable devices.

While these delays are typically applied by the PHY, some MACs support
configuring internal clock delay settings, too.  Hence add standardized
properties to configure this.

This is the MAC counterpart of commit 9150069b ("dt-bindings:
net: Add tx and rx internal delays"), which applies to the PHY.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>