logging: adsp hda backend improvements

* Adds a default hook and init function for cavstool.
* Adds an optional padding on flush feature to ensure all data is written.
* Fixes an error in cavstool.py for correctly wrapping the ring buffer.
* The test case now ensures wraps and flushes occur numerous times.

Signed-off-by: Tom Burdick <thomas.burdick@intel.com>