now that predicates have a decent abstraction layer on them, introduce a new

now that predicates have a decent abstraction layer on them, introduce a new
kind of predicate: one that is specific to imm nodes.  The predicate function
specified here just checks an int64_t directly instead of messing around with
SDNode's.  The virtue of this is that it means that fastisel and other things
can reason about these predicates.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129675 91177308-0d34-0410-b5e6-96231b3b80d8