octeon/generic: ubnt,erlite: define profile

octeon/generic: ubnt,erlite: define profile

Currently the erlite install shows Model as EBNT_E100, uses eth0 as lan,
eth1 as wan, and doesn't use eth2.

- define dts for this device, such that we get a cleaner naming here
- fix handing of this device to inlude eth2
- change eth0 to wan, like er-4/usg/etc as it once was intended

Fixes: https://github.com/openwrt/openwrt/issues/14946
Signed-off-by: Fabian Groffen <grobian@gentoo.org>
Link: https://github.com/openwrt/openwrt/pull/17758
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>