dt-bindings: timer: tpm-timer: Add imx8ulp compatible string

The tpm timer on i.MX8ULP is derived from i.MX7ULP, it use two
compatible strings, so update the compatible string for it.

Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/20211126074002.1535696-4-peng.fan@oss.nxp.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

Author: JackyBai

Documentation/devicetree/bindings/timer/nxp,tpm-timer.yaml

@@ -19,7 +19,11 @@ description: |
 
 properties:
   compatible:
-    const: fsl,imx7ulp-tpm
+    oneOf:
+      - const: fsl,imx7ulp-tpm
+      - items:
+          - const: fsl,imx8ulp-tpm
+          - const: fsl,imx7ulp-tpm
 
   reg:
     maxItems: 1