Mark the 64-bit x86 push/pop instructions as In64BitMode. Mark the corresponding 32-bit versions with the same encodings Not64BitMode. Remove hack from tablegen disassembler table emitter. Fix bad test.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@198530 91177308-0d34-0410-b5e6-96231b3b80d8