doc/opal-api: Document changes of adding interrupt-parent property un…

…der /ibm, opal/ipmi node on POWER9 and above.

Signed-off-by: Pridhiviraj Paidipeddi <ppaidipe@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

doc/opal-api/power9-changes.rst

@@ -21,6 +21,8 @@ Device Tree
 - ``/ibm,opal/`` compatible property now just lists ``ibm,opal-v3`` and no longer ``ibm,opal-v2`` (power9 and above only)
 - Use only ``stdout-path`` property from POWER9 and above as usage of ``linux,stdout-path`` is deprecated
 - Rename ``fsp-ipl-side`` as ``sp-ipl-side`` in ``/ipl-params``
+- Add interrupt-parent property for ``/ibm,opal/ipmi`` node on POWER9 and above
+  to make use of OPAL irqchip rather than event interface in linux.
 
 TODO
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