dt-bindings: PCI: imx6q-pcie: Add reg-name "dbi2" and "atu" for i.MX8M PCIe Endpoint

Add reg-name: "dbi2", "atu" for i.MX8M PCIe Endpoint.

For i.MX8M PCIe EP, the dbi2 and atu addresses are pre-defined in the
driver. This method is not good.

In commit b7d67c6130 ("PCI: imx6: Add iMX95 Endpoint (EP) support"),
Frank suggests to fetch the dbi2 and atu from DT directly. This commit is
preparation to do that for i.MX8M PCIe EP.

These changes wouldn't break driver function. When "dbi2" and "atu"
properties are present, i.MX PCIe driver would fetch the according base
addresses from DT directly. If only two reg properties are provided, i.MX
PCIe driver would fall back to the old method.

Link: https://lore.kernel.org/linux-pci/1723534943-28499-2-git-send-email-hongxing.zhu@nxp.com
Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>

Documentation/devicetree/bindings/pci/fsl,imx6q-pcie-ep.yaml

@@ -65,12 +65,14 @@ allOf:
     then:
       properties:
         reg:
-          minItems: 2
-          maxItems: 2
+          minItems: 4
+          maxItems: 4
         reg-names:
           items:
             - const: dbi
             - const: addr_space
+            - const: dbi2
+            - const: atu
 
   - if:
       properties:
@@ -129,8 +131,11 @@ examples:
 
     pcie_ep: pcie-ep@33800000 {
       compatible = "fsl,imx8mp-pcie-ep";
-      reg = <0x33800000 0x000400000>, <0x18000000 0x08000000>;
-      reg-names = "dbi", "addr_space";
+      reg = <0x33800000 0x100000>,
+            <0x18000000 0x8000000>,
+            <0x33900000 0x100000>,
+            <0x33b00000 0x100000>;
+      reg-names = "dbi", "addr_space", "dbi2", "atu";
       clocks = <&clk IMX8MP_CLK_HSIO_ROOT>,
                <&clk IMX8MP_CLK_HSIO_AXI>,
                <&clk IMX8MP_CLK_PCIE_ROOT>;