soc/intel_adsp: Add a cavs_ipc driver to manage host IPC

This is a slightly higher level Zephyr device that manages the host
IPC device for applications.  There's an interface to make synchronous
and asynchronous calls, to receive commands via (interrupt context)
callbacks and emit async "done" notifications after processing is
complete.  It should work for pretty much any application
architecture.

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