ARM: dts: imx6qdl-sabrelite: fix ENET group

GPIO16 is used for I2C3, not ENET_REF_CLK.
Also, remove pull-ups from tx pins, and ENET_MDIO
which has an external pull-up.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>