This patch implements the command handling mechanism. The digital stack
serializes all commands sent to the driver. This means that the digital
stack waits for the reply of the current command before sending a new
one. So there is no command queue managed at driver level.

All Port-100 commands are asynchronous. If the command has been sent
successfully to the device, it replies with an ACK frame. Then the
command response is received (or actually no-response in case of
timeout or error) and a command complete work on the system workqueue
is responsible for sending the response (or the error) back to the
digital stack.

The digital stack requires some commands to be synchronous, mainly
hardware configuration ones. These commands use the asynchronous
command path but are made synchronous by using a completion object.
Signed-off-by: Thierry Escande <thierry.escande@linux.intel.com>
Cc: Stephen Tiedemann <stephen.tiedemann@gmail.com>
Tested-by: Cho, Yu-Chen <acho@suse.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>