dt-bindings: add vendor prefix for edimax

Add vendor prefix for EDIMAX Technology Co., Ltd (https://www.edimax.com/

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Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>