hal:qap-test: Support for input buffer available event

-This change includes test app changes to support event
mechanasim for getting buffer availability.
-As soon as module has the free space to copy the input
buffer, it will raise an event to the testapp notifing that a
new buffer can be sent.
-This will replace the exising polling mechanasim,
where testapp periodically queries the module to check if
a new input buffer can be sent or not.

Change-Id: I84f6f8a574f2589643733b4543348ad7992208c5