COMPMID-3314: Enable OpenMP in the reference tests

Change-Id: I05b5fedb998317144e0dd13a6377a97207b27f46
Signed-off-by: Michalis Spyrou <michalis.spyrou@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/3024
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Michele Di Giorgio <michele.digiorgio@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
diff --git a/tests/validation/reference/QuantizationLayer.cpp b/tests/validation/reference/QuantizationLayer.cpp
index cfc5085..a70523d 100644
--- a/tests/validation/reference/QuantizationLayer.cpp
+++ b/tests/validation/reference/QuantizationLayer.cpp
@@ -50,12 +50,18 @@
     switch(output_data_type)
     {
         case DataType::QASYMM8:
+#if defined(_OPENMP)
+            #pragma omp parallel for
+#endif /* _OPENMP */
             for(int i = 0; i < src.num_elements(); ++i)
             {
                 dst[i] = quantize_qasymm8((src[i]), qinfo, rounding_policy);
             }
             break;
         case DataType::QASYMM8_SIGNED:
+#if defined(_OPENMP)
+            #pragma omp parallel for
+#endif /* _OPENMP */
             for(int i = 0; i < src.num_elements(); ++i)
             {
 #ifdef __aarch64__
@@ -66,6 +72,9 @@
             }
             break;
         case DataType::QASYMM16:
+#if defined(_OPENMP)
+            #pragma omp parallel for
+#endif /* _OPENMP */
             for(int i = 0; i < src.num_elements(); ++i)
             {
                 dst[i] = quantize_qasymm16((src[i]), qinfo, rounding_policy);