ARM: tegra: trimslice: Initialize PCIe from DT

With the device tree support in place, probe the PCIe controller from
the device tree and remove the corresponding workaround in the board
file.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>