print instruction encodings with the existing comment facilities,

print instruction encodings with the existing comment facilities,
so that llvm-mc -show-encoding prints like this:

	hlt                                                 ## encoding: [0xf4]

instead of like this:

	hlt
                     # encoding: [0xf4]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95207 91177308-0d34-0410-b5e6-96231b3b80d8