ARM: dts: imx6qdl: Remove #address/#size-cells from mipi_dsi

Remove unnecessary #address-cells/#size-cells to fix the following
DTC warnings:

arch/arm/boot/dts/imx6dl-apf6dev.dtb: Warning (avoid_unnecessary_addr_size): /soc/aips-bus@2100000/mipi@21e0000: unnecessary #address-cells/#size-cells without "ranges" or child "reg" property

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>