"When using crystal, the clock is generated internally after power is
stable. For a reliable power on reset, suggest to keep asserting the reset
low long enough (10ms) to ensure the clock is stable and clock-to-reset 1ms
requirement is satisfied."
Pass the 'reset-assert-us' property to describe such requirement.
While at it, use the 'reset-gpios' property inside the the mdio
node instead of the deprecated usage of 'phy-reset-gpios'.