dt-bindings: firmware: xilinx: Add conditional pinctrl schema

dt-bindings: firmware: xilinx: Add conditional pinctrl schema

Updates the Device Tree bindings for Xilinx firmware by introducing
conditional schema references for the pinctrl node.

Previously, the pinctrl node directly referenced
xlnx,zynqmp-pinctrl.yaml. However, this patch modifies the schema to
conditionally apply the correct pinctrl schema based on the compatible
property. Specifically:
- If compatible contains "xlnx,zynqmp-pinctrl", reference
  xlnx,zynqmp-pinctrl.yaml.
- If compatible contains "xlnx,versal-pinctrl", reference
  xlnx,versal-pinctrl.yaml.

Additionally, an example entry for "xlnx,versal-pinctrl" has been
added under the examples section.

Signed-off-by: Ronak Jain <ronak.jain@amd.com>
Link: https://patch.msgid.link/20251212100542.2756757-3-ronak.jain@amd.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>