ARM: dts: apalis-imx6qdl: use rgmii-id instead of rgmii

Until now a PHY-fixup in mach-imx set our rgmii timing correctly. For
the PHY KSZ9131 there is no PHY-fixup in mach-imx. To support this PHY
too, use rgmii-id.
For the now used KSZ9031 nothing will change, as rgmii-id is only
implemented and supported by the KSZ9131.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>