SOF auxiliary bus - Part 1

[ujfalusi]

Hi,

This is the first part of the reworked pull last sent by @fredoh9.
I have decided to split up the patches into at least two batch to make it easier to review and then fix up based on the comments.

The first part adds the basic support for the auxbus and introduces the term 'sof client'
The Kconfig has been changed so the the client support is selected by the user to keep things easier for the users.
It also includes the conversion of the first client: IPC flood test.
This is a generic test client so instead of doing the registration per architecture as it was in the first series we do it in the generic code. This will allow ARM to keep using it (it was available or them as well).
The Kconfig remained the same, but we now have option to have more than one IPC flood running at the same time. I have also made sure that we don't break testing scripts via debugfs.

Looking forward: the probe test will be converted along the same line as the IPC flood test as that one is also a generic test and it was (well, it is) available on ARM also.
On the Intel side we might drop most of the code for now until we can introduce the clients (HDMI, etc).
I believe the gdb and firmware debugging support might be also platform independent, but I need to check that and plan accordingly.

After addressing the surely coming comments I will include the probe test client into v2.