dt-bindings: PCI: ti,j721e-pci-host: Add ACSPCIE proxy control property

Add the "ti,syscon-acspcie-proxy-ctrl" device-tree property which is
used to obtain a reference to the ACSPCIE Proxy Control register along
with the details of the PAD IO Buffer output enable bits.

The ACSPCIE Proxy Control register is used to drive the reference clock
for the PCIe Endpoint device via the PAD IO Buffers of the ACSPCIE module.
The ACSPCIE module can be used as an alternative to either an on-board
clock generator or an external clock generator for providing the reference
clock to the PCIe Endpoint device.

Link: https://lore.kernel.org/linux-pci/20240829105316.1483684-2-s-vadapalli@ti.comSigned-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Documentation/devicetree/bindings/pci/ti,j721e-pci-host.yaml

@@ -38,6 +38,16 @@ properties:
       - const: reg
       - const: cfg
 
+  ti,syscon-acspcie-proxy-ctrl:
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+    items:
+      - items:
+          - description: Phandle to the ACSPCIE Proxy Control Register
+          - description: Bitmask corresponding to the PAD IO Buffer
+                         output enable fields (Active Low).
+    description: Specifier for enabling the ACSPCIE PAD outputs to drive
+                 the reference clock to the Endpoint device.
+
   ti,syscon-pcie-ctrl:
     $ref: /schemas/types.yaml#/definitions/phandle-array
     items: