dt-bindings: vendor-prefixes: Document EmbedFire

EmbedFire is a manufacturer of embed computers and education platform for
embed devices from Dongguan.

Add vendor prefix for it.

Signed-off-by: Wenhao Cui <lasstp5011@gmail.com>
Signed-off-by: Yuteng Zhong <zonyitoo@gmail.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/Y6Ud9MhRjCVAYMCj@VM-66-53-centos


Signed-off-by: Heiko Stuebner <heiko@sntech.de>