PCI: tegra: Move PCIe driver to drivers/pci/host

Move the PCIe driver from arch/arm/mach-tegra into the drivers/pci/host
directory. The motivation is to collect various host controller drivers
in the same location in order to facilitate refactoring.

The Tegra PCIe driver has been largely rewritten, both in order to turn
it into a proper platform driver and to add MSI (based on code by
Krishna Kishore <kthota@nvidia.com>) as well as device tree support.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
[swarren, split DT changes into a separate patch in another branch]
Signed-off-by: Stephen Warren <swarren@nvidia.com>