AMDGPU: Make worst-case assumption about the wait states in inline assembly

AMDGPU: Make worst-case assumption about the wait states in inline assembly

Summary:
Mesa still uses a hack where empty inline assembly is used as a kind of
optimization barrier. This exposed a problem where not enough wait states
were inserted, because the hazard recognizer implicitly assumed that each
inline assembly "instruction" has at least one wait state.

Reviewers: arsenm

Subscribers: kzhuravl, wdng, yaxunl, dstuttard, tpr, llvm-commits, t-tye

Differential Revision: https://reviews.llvm.org/D37205

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312635 91177308-0d34-0410-b5e6-96231b3b80d8