arm64: dts: freescale: imx8: Fix power controller name

The proper name is power-controller, not imx8qx-pd.

Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Signed-off-by: Viorel Suman <viorel.suman@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>