dt-bindings: remoteproc: imx_rproc: add i.MX7ULP support

Add i.MX7ULP compatible.

We use i.MX7ULP dual mode and in which case i.MX7ULP A7 core runs under
control of M4 core, M4 core starts by ROM and powers most services used
by A7 core, so A7 core has no power to start and stop M4 core. So
clocks and syscon are not required.
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/1620274123-1461-3-git-send-email-peng.fan@oss.nxp.comSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Documentation/devicetree/bindings/remoteproc/fsl,imx-rproc.yaml

@@ -18,6 +18,7 @@ properties:
       - fsl,imx8mq-cm4
       - fsl,imx8mm-cm4
       - fsl,imx7d-cm4
+      - fsl,imx7ulp-cm4
       - fsl,imx6sx-cm4
 
   clocks:
@@ -57,8 +58,6 @@ properties:
 
 required:
   - compatible
-  - clocks
-  - syscon
 
 additionalProperties: false