Kernel prepatch 5.12-rc8

In the end, Linus decided to hold the 5.12 release for one more week and
put out 5.12-rc8 instead. 'Ok, so it's been _fairly_ calm this past week, but it hasn't been the
kind of dead calm I would have taken to mean 'no rc8 necessary'.

So here we are, with an extra rc to make sure things are all settled
down.'