Add ARM64 CLS patterns

This patch adds patterns to generate the cls instruction ARM64. Includes tests
for 64 bit and 32 bit operands.

rdar://15611957

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206079 91177308-0d34-0410-b5e6-96231b3b80d8