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>

Documentation/devicetree/bindings/phy/phy-tegra194-p2u.txt

+NVIDIA Tegra194 P2U binding
+
+Tegra194 has two PHY bricks namely HSIO (High Speed IO) and NVHS (NVIDIA High
+Speed) each interfacing with 12 and 8 P2U instances respectively.
+A P2U instance is a glue logic between Synopsys DesignWare Core PCIe IP's PIPE
+interface and PHY of HSIO/NVHS bricks. Each P2U instance represents one PCIe
+lane.
+
+Required properties:
+- compatible: For Tegra19x, must contain "nvidia,tegra194-p2u".
+- reg: Should be the physical address space and length of respective each P2U
+       instance.
+- reg-names: Must include the entry "ctl".
+
+Required properties for PHY port node:
+- #phy-cells: Defined by generic PHY bindings.  Must be 0.
+
+Refer to phy/phy-bindings.txt for the generic PHY binding properties.
+
+Example:
+
+p2u_hsio_0: phy@3e10000 {
+	compatible = "nvidia,tegra194-p2u";
+	reg = <0x03e10000 0x10000>;
+	reg-names = "ctl";
+
+	#phy-cells = <0>;
+};