R600/SI: Set bits on SMRD instructions

Set mayStore = 0 and enable named operand table.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214194 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Add isMUBUF / isMTBUF

Also add missing comments about how the flags work.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214195 91177308-0d34-0410-b5e6-96231b3b80d8