dt-bindings: mmc: arm,pl18x: Document interrupt-names is ignored

Due to inconsistency of existing DTs regarding the content of this IP
interrupt-names DT property, document this such that interrupt-names
is not used by this IP bindings.
Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20221013221242.218808-1-marex@denx.deSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Documentation/devicetree/bindings/mmc/arm,pl18x.yaml

@@ -95,7 +95,9 @@ properties:
       PIO (polled I/O) interrupt and occurs when the FIFO needs to be
       emptied as part of a bulk read from the card. Some variants have these
       two interrupts wired into the same line (logic OR) and in that case
-      only one interrupt may be provided.
+      only one interrupt may be provided. The interrupt-names property is
+      not used due to inconsistency of existing DTs regarding its content.
+    deprecated: false
     minItems: 1
     maxItems: 2