[Sound-open-firmware] Fallback on failed custom firmware loading

Hello Pierre,

I was wondering if this feature would be ok with you. We are working to start switching out various firmware files using command line boot params. Given we are doing this in AP firmware, we have no indication of what is in the OS and if the device has been loaded with a non-standard image. We clearly don't want to break audio for users who are running vanilla linux on these machines. So what my proposal is, if a firmware/topology path is passed in via module params is not found, that we fall back to the next method (dmi check) and lastly using the default rather than doing a one shot method. What are your thoughts here?