octeon: add SUPPORTED_DEVICES to er/erlite

octeon: add SUPPORTED_DEVICES to er/erlite

Using the BOARD_NAME variable results for both er and erlite devices to
identify themselfs as `er` and `erlite` (via `ubus call system board`).

This is problematic when devices search for firmware upgrades since the
OpenWrt profile is actually called `ubnt_edgerouter` and
`ubnt_edgerouter-lite`.

By adding the `SUPPORTED_DEVICE` a mapping is created to point devices
called `er` or `erlite` to the corresponding profile.

FIXES: https://github.com/openwrt/asu/issues/348

Signed-off-by: Paul Spooren <mail@aparcar.org>