soc/intel_adsp: Add unified "cavstool" loader/logger script

The existing scripting for these platforms has gotten a little stale.
The loader had bifurcated into a v15 and v25 variant, both of which
lived in the cavs15 board directory.  Building off Shao Ming's
excellent (if somewhat surprisingly committed) rework to unify
unchanged parts of the scripts, let's finish the job.

This adds a "cavstool.py" script with the following advantages:

+ It's just one script for everything, with a single unified load
  process that works reliably on both 1.5 and 1.8+ hardware.

+ It runs on all cAVS platforms (with a compatible kernel, those
  requirements haven't changed)

+ It automatically emitts logging synchronously after loading,
  eliminating the race between adsplog.py and cavs-fw.py where you
  could see logging from a previous test run.

+ It automatically detects and unloads a linux kernel module managing
  the same device (even if SOF has renamed the module again, heh).

+ Timings have been tuned up in general, it's about 2 seconds faster
  to get to first log output now.

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