ARM: dts: imx6qdl: Add power-domain phandle to CODA device node

The CODA960 VPU is part of the PU power domain. Add power-domains
phandle so it can be associated with the PU generic pm domain for
power gating.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>