soc/intel_adsp: cavstool: add support for DSP power state: D3

Change some behaviors when --log-only is passed in order to add support
for DSP power state: D3. This makes it possible to keep `cavstool
--log-only` running permanently in the "real-world" use case where the
Linux kernel loads the firmware and powers down audio when not in use.

More specifically:
- Do not disable D3 when using --log-only.
- Wait forever for the FW at boot time.
- Check live status when an invalid IPC is received and wait forever if
  not alive.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>