arm64: dts: freescale: imx8dxl: fix sc_pwrkey's property name linux,keycode

linux,keycode should be "linux,keycodes" according binding-doc
Documentation/devicetree/bindings/input/fsl,scu-key.yaml

Fixes: f537ee7f ("arm64: dts: freescale: add i.MX8DXL SoC support")
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>