[AArch64] Fix fast-isel of cbz of i1, i8, i16

[AArch64] Fix fast-isel of cbz of i1, i8, i16

This fixes a miscompilation in the AArch64 fast-isel which was
triggered when a branch is based on an icmp with condition eq or ne,
and type i1, i8 or i16. The cbz instruction compares the whole 32-bit
register, so values with the bottom 1, 8 or 16 bits clear would cause
the wrong branch to be taken.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220553 91177308-0d34-0410-b5e6-96231b3b80d8