[AArch64][FastISel] Don't even try to select vector icmps.

[AArch64][FastISel] Don't even try to select vector icmps.

We used to try to constant-fold them to i32 immediates.
Given that fast-isel doesn't otherwise support vNi1, when selecting
the result users, we'd fallback to SDAG anyway.
However, if the users were in another block, we'd insert broken
cross-class copies (GPR32 to FPR64).

Give up, let SDAG agree with itself on a vNi1 legalization strategy.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@252364 91177308-0d34-0410-b5e6-96231b3b80d8