ARM: dts: imx: Add support for DH electronics i.MX8M Plus DHCOM and PDK2

Add support for DH electronics i.MX8M Plus DHCOM SoM on PDK2 carrier board.
Currently supported are serial console, EQoS and FEC ethernets, eMMC, SD,
SPI NOR and USB 3.0 host.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>