ARM: dts: imx6qdl: use DT macro for clock ID

Switch to use DT macro for clock ID, so that device tree source is more
readable.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

diff --cc arch/arm/boot/dts/imx6dl.dtsi
Simple merge

diff --cc arch/arm/boot/dts/imx6q.dtsi
Simple merge

diff --cc arch/arm/boot/dts/imx6qdl.dtsi
Simple merge