ASoC: SOF: IPC client infrastructure

Merge series from Peter Ujfalusi <peter.ujfalusi@linux.intel.com>:

The Linux SOF implementation is historically monolithic in a sense that all
features accessible in the firmware can be used via the snd_sof_dev struct in
one way or another.

Support for features can not be added or removed runtime and with the current
way of things it is hard if not impossible to implement support for dynamic
feature support when based on the firmware manifest we can easily enable/access
independent modules with the SOF.

In order to be able to support such modularity this series introduces a small
framework within SOF for client support using the Auxiliary bus.

Client drivers can be removed runtime and later re-loaded if needed without
affecting the core's behaviour, but it is the core's and the platform's duty
to create the Auxiliary devices usable in the platform and via the firmware.

There is still a need for SOF manifest update to convey information about
features to really make the full dynamic client device creation.

The series will introduce the core SOF client support and converts the generic
ipc flood test, ipc message injector and the probes (Intel HDA only) to a client
driver.