apalis_t30: enable gigabit ethernet via pcie

Now with all the Tegra PCIe and Intel E1000 gigabit Ethernet driver
updates being merged actually make use of it.

While at it get rid of the USB networking support which now does not
make much sense any longer.

Signed-off-by: Marcel Ziswiler <marcel@ziswiler.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>