econet: basic Ethernet support

econet: basic Ethernet support

This is about as simple as it gets, it's able to start up and put
the onboard switch into dumb switch mode and then send untagged
frames which become available on every switch port.

It is out-of-tree to allow for rapid development and it is being
proposed now because even in this state it brings a lot of value
to the EcoNet platform and it is a fairly complex ethernet system
so it will take some time before the driver is in a state that
may be considered for upstreaming.

Signed-off-by: Caleb James DeLisle <cjd@cjdns.fr>
Link: https://github.com/openwrt/openwrt/pull/20685
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>