New SFB subsets are being added with the scheduler class name as a
suffix, so now is the time to go back to the base extension and add IALU
to its name.
This also:
- Drops a hyphen from the other SFB features for mul and minmax, to more
closely match their scheduling classes.
- Updates the predicates on specific SFB pseudos so we get verifier
errors if we introduce the pseudos when we don't have the right
subtarget feature.
- Updates the SFB Documentation comment to make it no longer
SiFive-specific.
a15a6c870b