dt-bindings: arm: imx: update fsl.yaml for imx8dxl

i.MX8DXL is a device targeting the automotive and industrial market
segments. The chip is designed to achieve both high performance and
low power consumption. It has a dual (2x) Cortex-A35 processor.

Signed-off-by: Shenwei Wang <shenwei.wang@nxp.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>