arm64: dts: imx8mp-kontron-dl: change touchscreen power-supply to AVDD28-supply

Update the touchscreen power-supply from 'power-supply' to 'AVDD28-supply' and
'VDDIO-supply' as per the binding documentation in goodix.yaml.

Fix below warning:
arch/arm64/boot/dts/freescale/imx8mp-kontron-dl.dtb: touchscreen@5d:
    'power-supply' does not match any of the regexes: 'pinctrl-[0-9]+'
        from schema $id: http://devicetree.org/schemas/input/touchscreen/goodix.yaml



Signed-off-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>