dt-bindings: Add vendor prefix for ROCKTECH DISPLAYS LIMITED

Add ROCKTECH DISPLAYS LIMITED (https://rocktech.com.hk) LCD panel
supplier.
Signed-off-by: Guido Günther <agx@sigxcpu.org>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -310,6 +310,7 @@ ricoh	Ricoh Co. Ltd.
 rikomagic	Rikomagic Tech Corp. Ltd
 riscv	RISC-V Foundation
 rockchip	Fuzhou Rockchip Electronics Co., Ltd
+rocktech	ROCKTECH DISPLAYS LIMITED
 rohm	ROHM Semiconductor Co., Ltd
 roofull	Shenzhen Roofull Technology Co, Ltd
 samsung	Samsung Semiconductor