Pass 'fsl,imx8dl-scu-pd' to fix the following schema warning:

system-controller: power-controller:compatible:0: 'fsl,scu-pd' is not one of ['fsl,imx8qm-scu-pd', 'fsl,imx8qxp-scu-pd']
	from schema $id: http://devicetree.org/schemas/firmware/fsl,scu.yaml#Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>