dt-bindings: Add Vendor prefix for Einfochips

Add devicetree vendor prefix for Einfochips.
https://www.einfochips.com/



Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>