zephyr-openthread-rcp: Support nrf52840-mdk-usb-dongle machine

This makerdiary board can be a fallback option for Oniro's gateway-blueprint
I've been tested it myself along my single arduino-nano node

Relate-to: eclipse/oniro-blueprints/transparent-gateway/meta-oniro-blueprints-gateway#6
Relate-to: https://gitlab.eclipse.org/pcoval/oniro-presentations/-/wikis/openthread
Forwarded: https://lists.yoctoproject.org/g/yocto/message/58209?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3ACreated%2C%2Cposterid%3A6590488%2C20%2C2%2C0%2C93972038


Signed-off-by: Philippe Coval <philippe.coval.ext@huawei.com>