ARM: dts: imx6qdl-apalis: mux HDMI CEC pin

Mux the HDMI CEC pin to make HDMI CEC working. With this change HDMI CEC
seems to work fine on a Apalis iMX6 on Ixora using cec-ctl.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>