R600/SI: Move setting of the lds bit to the base MUBUF class

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223721 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Set MayStore = 0 on MUBUF loads

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223722 91177308-0d34-0410-b5e6-96231b3b80d8