pci: tegra: correctly program PADS_REFCLK registers

The value that should be programmed into the PADS_REFCLK register varies
per SoC. Fix the Tegra PCIe driver to program the correct values. Future
SoCs will require different values in cfg0/1, so the two values are stored
separately in the per-SoC data structures.

For reference, the values are all documented in NV bug 1771116 comment 20.
The Tegra210 value doesn't match the current TRM, but I've filed a bug to
get the TRM fixed. Earlier TRMs don't document the value this register
should contain, but the ASIC team has validated all these values, except
for the Tegra20 value which is simply left unchanged in this patch.

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