net: phy: at803x: disable delay only for RGMII mode

Per "Documentation/devicetree/bindings/net/ethernet.txt" RGMII mode
should not have delay in PHY whereas RGMII_ID and RGMII_RXID/RGMII_TXID
can have delay in PHY.

So disable the delay only for RGMII mode and enable for other modes.
Also treat the default case as disabled delays.

Fixes: cd28d1d6

: ("net: phy: at803x: Disable phy delay for RGMII mode")
Reported-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Niklas Cassel <niklas.cassel@linaro.org>
Tested-by: Peter Ujfalusi <peter.ujflausi@ti.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>