Refactor the ScalarTargetTransformInfo API for querying about the
legality of an address mode to not use a struct of four values and
instead to accept them as parameters. I'd love to have named parameters
here as most callers only care about one or two of these, but the
defaults aren't terribly scary to write out.

That said, there is no real impact of this as the passes aren't yet
using STTI for this and are still relying upon TargetLowering.