ARM: tegra: Enable PCIe on Beaver

The Beaver has an ethernet NIC connected to the PCIe bus. Enable the
PCIe controller and the network device driver so that the device can
boot over the network.

In addition the board has a mini-PCIe expansion slot.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>