tegra: remove CONFIG_USB_ETHER_SMSC95XX from boards without it

The SMSC95xx series may exist either directly on a main board, or as a USB
to Ethernet dongle. However, dongles containing these chips are very rare.
Hence, remove this config option, except on Harmony where such a chip is
actually present on the board.

The asix option remains, since it's a popular chip, and I actively use a
dongle containing this.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>