dt-bindings: PCI: intel,lgm-pcie: Add 'atu' resource

The 'atu' information is already set in the dwc core, if it is specified in
the devicetree. The driver uses its own default, if not set in the
devicetree. This information is hardware-specific and should therefore be
maintained in the devicetree rather than in the source.

To be backward compatible, this field is not mandatory. If 'atu' resource
is not specified in the devicetree, the driver’s default value is used.

Signed-off-by: Florian Eckert <fe@dev.tdt.de>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260417-pcie-intel-gw-v5-7-0a2b933fe04f@dev.tdt.de

Documentation/devicetree/bindings/pci/intel-gw-pcie.yaml

@@ -27,16 +27,20 @@ properties:
       - const: snps,dw-pcie
 
   reg:
+    minItems: 3
     items:
       - description: Controller control and status registers.
       - description: PCIe configuration registers.
       - description: Controller application registers.
+      - description: Internal Address Translation Unit (iATU) registers.
 
   reg-names:
+    minItems: 3
     items:
       - const: dbi
       - const: config
       - const: app
+      - const: atu
 
   ranges:
     maxItems: 1
@@ -95,8 +99,9 @@ examples:
       #size-cells = <2>;
       reg = <0xd0e00000 0x1000>,
             <0xd2000000 0x800000>,
-            <0xd0a41000 0x1000>;
-      reg-names = "dbi", "config", "app";
+            <0xd0a41000 0x1000>,
+            <0xd0ec0000 0x1000>;
+      reg-names = "dbi", "config", "app", "atu";
       linux,pci-domain = <0>;
       max-link-speed = <4>;
       bus-range = <0x00 0x08>;