CMSIS-NN: Add support for int16 DSP avg pooling (#1486)

* CMSIS-NN: Add support for int16 DSP avg pooling


diff --git a/ARM.CMSIS.pdsc b/ARM.CMSIS.pdsc
index c9f1d3f..b2813bd 100644
--- a/ARM.CMSIS.pdsc
+++ b/ARM.CMSIS.pdsc
@@ -12,6 +12,7 @@
       Active development ...
       CMSIS-NN: 4.0.0 (see revision history for details)
        - Changed return types of all API's
+       - Support for int16 average pooling DSP implementation
     </release>
     <release version="5.9.0" date="2022-05-02">
       CMSIS-Core(M): 5.6.0