AMDGPU/GFX10: Apply the VMEM-to-scalar-write hazard also to writes to EXEC

Summary: Change-Id: I854fbf7d48e937bef9f8f3f5d0c8aeb970652630

Reviewers: rampitec, mareko

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D64807

Change-Id: I4405b3a7f84186acea5a78d291bff71056e745fc
llvm-svn: 366314