dt-bindings: PHY: P2U: Add Tegra194 P2U block

Add support for Tegra194 P2U (PIPE to UPHY) module block which is a glue
module instantiated once for each PCIe lane between Synopsys DesignWare
core based PCIe IP and Universal PHY block.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Thierry Reding <treding@nvidia.com>
Acked-by: Kishon Vijay Abraham I <kishon@ti.com>