[SelectionDAG] Assert on the width of DemandedElts argument to computeKnownBits for all vector typed operations not just build_vector.

Fix AArch64 unit test that fails with the assertion added.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346437 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed