dt-bindings: Add ITE Tech prefix

Add vendor prefix for ITE Tech Inc, http://www.ite.com.tw/

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Sean Cross <xobs@kosagi.com>
Cc: devicetree@vger.kernel.org
To: dri-devel@lists.freedesktop.org
Signed-off-by: Rob Herring <robh@kernel.org>