ASoC: SOF: IPC path handling and fallback support

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

The main aim of the series is to provide a mechanism to fallback to 'older' IPC
versions in case the desired one is missing either a firmware or topology file.
It is going to make the life of users and distributions if we are going to
start transition existing IPC3 platforms to IPC4 (CAVS2.5) and we might have
missed some topology file to convert for example.
In that case the kernel will fallback to IPC3 without audio regression.

To be able to support this we needed to change the probe sequence to know the
topology filename earlier and check if it is present in the filesystem.

No functional changes for now, the default IPC versions have not been changed.