ARM: dts: uniphier: Change phy-mode to RGMII-ID to enable delay pins for RTL8211E

UniPhier PXs2 boards have RTL8211E ethernet phy, and the phy have the RX/TX
delays of RGMII interface using pull-ups on the RXDLY and TXDLY pins.

After the commit bbc4d71d ("net: phy: realtek: fix rtl8211e rx/tx
delay config"), the delays are working correctly, however, "rgmii" means
no delay and the phy doesn't work. So need to set the phy-mode to
"rgmii-id" to show that RX/TX delays are enabled.

Fixes: e3cc9319 ("ARM: dts: uniphier: add AVE ethernet node")
Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: David S. Miller <davem@davemloft.net>