dt-bindings: PCI: tegra: Add PCIe slot supplies regulator entries

Add optional bindings "vpcie3v3-supply" and "vpcie12v-supply" to describe
regulators of a PCIe slot's supplies 3.3V and 12V provided the platform
is designed to have regulator controlled slot supplies.
Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Thierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/pci/nvidia,tegra194-pcie.txt

@@ -104,6 +104,12 @@ Optional properties:
    specified in microseconds
 - nvidia,aspm-l0s-entrance-latency-us: ASPM L0s entrance latency to be
    specified in microseconds
+- vpcie3v3-supply: A phandle to the regulator node that supplies 3.3V to the slot
+  if the platform has one such slot. (Ex:- x16 slot owned by C5 controller
+  in p2972-0000 platform).
+- vpcie12v-supply: A phandle to the regulator node that supplies 12V to the slot
+  if the platform has one such slot. (Ex:- x16 slot owned by C5 controller
+  in p2972-0000 platform).
 
 Examples:
 =========
@@ -156,6 +162,8 @@ Tegra194:
 			  0xc2000000 0x18 0x00000000 0x18 0x00000000 0x4 0x00000000>;  /* prefetchable memory (16GB) */
 
 		vddio-pex-ctl-supply = <&vdd_1v8ao>;
+		vpcie3v3-supply = <&vdd_3v3_pcie>;
+		vpcie12v-supply = <&vdd_12v_pcie>;
 
 		phys = <&p2u_hsio_2>, <&p2u_hsio_3>, <&p2u_hsio_4>,
 		       <&p2u_hsio_5>;