dt-bindings: dsp: fsl,dsp: document 'access-controllers' property

Some DSP instances may have their access to certain peripherals
conditioned by a bus access controller such as the one from the
AIPSTZ bridge.

Add the optional 'access-controllers' property, which may be used
in such cases.

Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Author: LaurentiuM1234

Documentation/devicetree/bindings/dsp/fsl,dsp.yaml

@@ -91,6 +91,9 @@ properties:
       - const: runstall
       - const: softreset
 
+  access-controllers:
+    maxItems: 1
+
 required:
   - compatible
   - reg