arch-vega: Mark global instructions executed as global

The executed_as field is currently not set for global memory
instructions. This results in the default of SC_NONE, causing the status
vector to be all zeros. The GM pipe sees this and completes the
instruction immediately rather than issuing memory requests. This is
fixed by marking the instruction as executed as SC_GLOBAL always. Flat
instructions use resolvedFlatSegment for this, however since global
instructions are known to be global we can set this field directly. This
results in the expected issuing of memory requests to GPU memory.

Change-Id: Ic23102853ccd49a41e2f083b7bb24f033dfed18a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/57829
Reviewed-by: Matt Sinclair <mattdsinclair@gmail.com>
Maintainer: Matt Sinclair <mattdsinclair@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/amdgpu/vega/insts/op_encodings.hh

@@ -931,6 +931,9 @@ namespace VegaISA
 
             if (isFlat()) {
                 gpuDynInst->resolveFlatSegment(gpuDynInst->exec_mask);
+            } else {
+                gpuDynInst->staticInstruction()->executed_as =
+                    enums::SC_GLOBAL;
             }
         }