ARM: ISB cannot be passed the same options as DMB

ISB should only accepts full system sync, other options are reserved

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183656 91177308-0d34-0410-b5e6-96231b3b80d8
Fix misleading comments in ARMAsmParser

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183657 91177308-0d34-0410-b5e6-96231b3b80d8
Update for current naming conventions.

I will change identifyFileType to use a StringRef in the next patch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@183664 91177308-0d34-0410-b5e6-96231b3b80d8