dt-bindings: PCI: Add bindings for Brcmstb EP voltage regulators

Add bindings for Brcmstb EP voltage regulators.  A new mechanism is to be
added to the Linux PCI subsystem that will allocate and turn on/off
regulators.  These are standard regulators -- vpcie12v, vpcie3v3, and
vpcie3v3aux -- placed in the DT in the bridge node under the host bridge
device.

The use of a regulator property in the PCIe EP subnode such as
"vpcie12v-supply" depends on a pending pullreq to the pci-bus.yaml
file at

  devicetree-org/dt-schema#63

Link: https://lore.kernel.org/r/20220106160332.2143-4-jim2101024@gmail.com
Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>

Author: jim2101024

Documentation/devicetree/bindings/pci/brcm,stb-pcie.yaml

@@ -159,5 +159,24 @@ examples:
                                  <0x42000000 0x1 0x80000000 0x3 0x00000000 0x0 0x80000000>;
                     brcm,enable-ssc;
                     brcm,scb-sizes =  <0x0000000080000000 0x0000000080000000>;
+
+                    /* PCIe bridge, Root Port */
+                    pci@0,0 {
+                            #address-cells = <3>;
+                            #size-cells = <2>;
+                            reg = <0x0 0x0 0x0 0x0 0x0>;
+                            compatible = "pciclass,0604";
+                            device_type = "pci";
+                            vpcie3v3-supply = <&vreg7>;
+                            ranges;
+
+                            /* PCIe endpoint */
+                            pci-ep@0,0 {
+                                    assigned-addresses =
+                                        <0x82010000 0x0 0xf8000000 0x6 0x00000000 0x0 0x2000>;
+                                    reg = <0x0 0x0 0x0 0x0 0x0>;
+                                    compatible = "pci14e4,1688";
+                            };
+                    };
             };
     };