of: Add vendor prefix for BOE Technology Group

BOE Technology Group Co., Ltd. is a supplier of semiconductor display
technologies, products and services.

Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
[treding@nvidia.com: add commit message, fixup subject]
Signed-off-by: Thierry Reding <treding@nvidia.com>