Release lock on thread yield during blit ops

Thread yield doesn't drop the scoped acquired mutex so drop it around
yield to prevent a multithread deadlock.

Change-Id: Ie21f3bff89f6f9e4c57e5b3ccf17968f253fa23a


[ROCm/ROCR-Runtime commit: 70f0a44910]

projects/rocr-runtime/runtime/hsa-runtime/core/runtime/amd_gpu_agent.cpp

@@ -829,7 +829,9 @@ hsa_status_t GpuAgent::DmaCopy(void* dst, const void* src, size_t size) {
 void GpuAgent::SetCopyRequestRefCount(bool set) {
   ScopedAcquire<KernelMutex> lock(&blit_lock_);
   while (pending_copy_stat_check_ref_) {
+    blit_lock_.Release();
     os::YieldThread();
+    blit_lock_.Acquire();
   }
   if (!set && pending_copy_req_ref_) pending_copy_req_ref_--;
   else pending_copy_req_ref_++;
@@ -838,7 +840,9 @@ void GpuAgent::SetCopyRequestRefCount(bool set) {
 void GpuAgent::SetCopyStatusCheckRefCount(bool set) {
   ScopedAcquire<KernelMutex> lock(&blit_lock_);
   while (pending_copy_req_ref_) {
+    blit_lock_.Release();
     os::YieldThread();
+    blit_lock_.Acquire();
   }
   if (!set && pending_copy_stat_check_ref_) pending_copy_stat_check_ref_--;
   else pending_copy_stat_check_ref_++;