dt-bindings: fsl: add imx7ulp system integration module binding

Add i.MX7ULP system integration module (SIM) binding.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>