arm64: dts: ti: j721e-som/common-proc-board: Add product links

Add product links to get reference to schematics and design files
Signed-off-by: Nishanth Menon <nm@ti.com>
Link: https://lore.kernel.org/r/20230601183151.1000157-4-nm@ti.comSigned-off-by: Vignesh Raghavendra <vigneshr@ti.com>

arch/arm64/boot/dts/ti/k3-j721e-common-proc-board.dts

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2019 Texas Instruments Incorporated - https://www.ti.com/
+ *
+ * Product Link: https://www.ti.com/tool/J721EXCPXEVM
  */
 
 /dts-v1/;

arch/arm64/boot/dts/ti/k3-j721e-som-p0.dtsi

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2019-2020 Texas Instruments Incorporated - https://www.ti.com/
+ *
+ * Product Link: https://www.ti.com/tool/J721EXSOMXEVM
  */
 
 /dts-v1/;