WIP: DPDMUX/DPAA2 dynamic setup

Putting this here for now as this is very new and could change completely.

See https://gitlab.com/traversetech/muvirt/-/wikis/DPDMUX

Currently implemented:

• Creation of a DPDMUX with DPMAC uplink at boot
• Attach and detach (after /etc/init.d/muvirt stop <vmname>) of a VM port to DPDMUX

Not currently implemented (you can do this with manual DPRC containers):

• direct DPNI/DPMAC assignment to VM
• Back-to-back DPNIs ("chaining") between two VMs
• information calls in the dpaa2 ubus/rpcd service

Also not done yet:

• Mark DPAA2 capable VMs in appliance store and allow certain Ten64-only appliances (such as OpenWrt) to be used as a VM.

MC firmware 10.20 or later is recommended, interoperability issues could arise if an earlier version is used.