arm: dts: imx6qdl-udoo: fix rgmii phy-mode for ksz9031 phy

Commit bcf3440c ("net: phy: micrel: add phy-mode support for the
KSZ9031 PHY") fixed micrel phy driver adding proper support for phy
modes. Adapt imx6q-udoo board phy settings : explicitly set required
delay configuration using "rgmii-id".

Fixes: cbd54fe0 ("ARM: dts: imx6dl-udoo: Add board support based off imx6q-udoo")
Signed-off-by: Sergey Matyukevich <geomatsi@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>