Draft: import patches from sdm670-linux

It's still a long way before this MR can be merged. Writing down some of the points I'm thinking at the moment:

• testing in a Mobian system on real device
• rearrange the patches of the sdm670 sub-folder so that those are numbered by area instead of chronologically... if this would have been done in the first step, the analysis would have been much easier. I'd like to prepare a table as a summary of this import
• I will need some support from experienced folks about some q6voice-related patches I had to drop because the sdm845-mainline and sdm670-mainline folks took different approaches, then it's not as easy as choosing the most complete one... this point will be clearer after having the table of the previous point ready
• cleaning up the branch, squashing some commit
• fixing audio
• check nothing getting broken on sdm845 devices in the process