[Sparc] Add membar assembler tags

Summary: The Sparc V9 membar instruction can enforce different types of
memory orderings depending on the value in its immediate field.  In the
architectural manual the type is selected by combining different assembler
tags into a mask. This patch adds support for these tags.

Reviewers: jyknight, venkatra, brad

Reviewed By: jyknight

Subscribers: fedor.sergeev, jrtc27, jfb, llvm-commits

Differential Revision: https://reviews.llvm.org/D53491

llvm-svn: 349048