ARM: tegra: enable PCIe controller on p2771-0000

ARM: tegra: enable PCIe controller on p2771-0000

p2771-0000 has a couple of PCIe ports; one physically x4 desktop PCI
connector (which may run at x2 electrically, depending on the board
version and configuration) and a x1 connection to the M.2 slot (which may
not be active, depending on the board version and configuration). This
change enables those.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>