boards: teensy4: Update config for ethernet

- Updates teensy board configs for use with new `eth_nxp_enet.c` driver
- Remove ethernet configs from teensy40 (4.0 has no ethernet phy)
- Adds a device entry to include `tests/drivers/build_all/ethernet/`

Signed-off-by: Bernhard Krämer <bdkrae@gmail.com>