ARM: dts: am335x-evm: Fix PHY mode for ethernet

The PHY must add both tx and rx delay and not only on the tx clock.
The board uses AR8031_AL1A PHY where the rx delay is enabled by default,
the tx dealy is disabled.

The reason why rgmii-txid worked because the rx delay was not disabled by
the driver so essentially we ended up with rgmii-id PHY mode.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>