PCI: tegra: Implement PCA enable workaround

Tegra210's PCIe controller has a bug that requires the PCA (performance
counter) feature to be enabled. If this isn't done, accesses to device
configuration space will hang the chip for tens of seconds. Implement the
workaround.

Based on commit 514e19138af2 ("pci: tegra: implement PCA enable
workaround") from U-Boot by Stephen Warren <swarren@nvidia.com>.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Bjorn Helgaas <helgaas@kernel.org>