tests/intel_adsp: MP core power fixups for older cAVS platforms

On cAVS before 2.5, core power was controlled by the host.  Add a
command to the cavstool.py script to allow us to do that under test
command so we can exercise multiprocessor startup/shutdown outside of
SOF.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>

soc/xtensa/intel_adsp/tools/cavstool.py

@@ -336,6 +336,8 @@ def ipc_command(data, ext_data):
             asyncio.ensure_future(ipc_delay_done())
     elif data == 2: # echo back ext_data as a message command
         send_msg = True
+    elif data == 3: # set ADSPCS
+        dsp.ADSPCS = ext_data
     else:
         log.warning(f"cavstool: Unrecognized IPC command 0x{data:x} ext 0x{ext_data:x}")