ARM & AArch64: combine implementation of vcaXYZ intrinsics

Now that the back-end intrinsics are more regular, there's no need for the
special handling these got in the front-end, so they can be moved to
EmitCommonNeonBuiltinExpr.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200769 91177308-0d34-0410-b5e6-96231b3b80d8