dt-bindings: vendor-prefixes: Add Longcheer Technology Co., Ltd.

Add the "longcheer" vendor prefix for Longcheer Technology Co., Ltd.,
an "industry-leading service provider of mobile phone design
and product delivery". (http://www.longcheer.com

)

Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>