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

Origin: https://gitlab.eclipse.org/eclipse/oniro-core/meta-zephyr/-/merge_requests/22
Relate-to: https://gitlab.eclipse.org/eclipse/oniro-blueprints/transparent-gateway/meta-oniro-blueprints-gateway/-/issues/6
Relate-to: https://gitlab.eclipse.org/pcoval/oniro-presentations/-/wikis/openthread
Forwarded: https://lists.yoctoproject.org/g/yocto/search?q=posterid:6590488
Signed-off-by: Philippe Coval <philippe.coval@astrolabe.coop>
Signed-off-by: Philippe Coval <philippe.coval.ext@huawei.com>