arm64: dts: imx8mp: Add HW variant details to i.MX8M Plus DHCOM PDK2

Add information about which exact SoM variant is used on which PDK2 variant.
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@denx.de>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Shawn Guo <shawnguo@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mp-dhcom-pdk2.dts

 // SPDX-License-Identifier: (GPL-2.0+ OR MIT)
 /*
  * Copyright (C) 2022 Marek Vasut <marex@denx.de>
+ *
+ * DHCOM iMX8MP variant:
+ * DHCM-iMX8ML8-C160-R409-F1638-SPI16-GE-CAN2-SD-RTC-WBTA-ADC-T-RGB-CSI2-HS-I-01D2
+ * DHCOM PCB number: 660-100 or newer
+ * PDK2 PCB number: 516-400 or newer
  */
 
 /dts-v1/;