mav@ pointed out a problem with the mapping code in the mps driver where devices were not getting mapped due to no space available. After looking into this, I found multiple problems with the mapping code, so this turned into quite a big change. I plan on getting this into 11.1. I added a lot of comments which were missing so hopefully that helps in the review. I basically copied the changes that I did for mpr(4) over to mps(4). Refer to review #10861 for the mpr(4) changes.

I tested most everything using the mpr(4) driver instead of this mps(4) driver. But I did do some sanity checks to make sure some of the mapping was working as expected for mps(4).