intel_adsp: cavs: add gdb support

Uses SRAM debug region to pass GDB messages to host, which is exposed
via PTY by cavstool with -d arg or using the SOF kernel driver via a
debugfs file.

Signed-off-by: Noah Klayman <noah.klayman@intel.com>
[guennadi.liakhovetski@linux.intel.com: update to current "main"]
Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>