tools: debug_stream.py: debug_stream record receiving and decoding

Python implementation for receiving and decoding debug-stream records
from debug window slot transportation. Opens SOF debugfs file
"debug_stream" reads and decodes the records from the circular buffer
documented in soc_debug_window_slot.h. This initial version only knows
of DEBUG_STREAM_RECORD_ID_THREAD_INFO records.

Signed-off-by: Jyri Sarha <jyri.sarha@linux.intel.com>