soc/intel_adsp: Update cavs-fw.py loader for cAVS 2.5 devices

Add a loader script variant for Tiger Lake (cAVS 2.5) devices, which
have very slightly different loading behavior from older 1.5 DSPs.

This is added as a "-v25.py" script, and the original has been renamed
to cavs-fw-v15.py.  Note that there is no good reason except schedule
pressure that these are not the same script, I just wasn't able to
make a single script work compatibly in the time available.

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