PCI: tegra: Overhaul regulator usage

The current usage of regulators for the Tegra PCIe block is wrong. It
doesn't accurately reflect the actual supply inputs of the IP block and
therefore isn't as flexible as it should be. Rectify this by describing
all possible supply inputs in the device tree binding documentation and
deprecate the old supply properties.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>