dt-bindings: Add vendor prefix for PHICOMM Co., Ltd.

PHICOMM Co., Ltd. is a hardware provider headquartered in Shanghai, it's
product includes router and smart devices.

Signed-off-by: He Yangxuan <yangxuan8282@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>