AArch64: switch patterns to be type-based rather than RegClass-based

It's a bit of churn in the blame log, but I think there are real benefits to
the newer system so I'm making the change in one go.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178633 91177308-0d34-0410-b5e6-96231b3b80d8