Break up core/Utils.h to reduce unused code being included everywhere

Makes a small difference to compile times and opens up other opportunities
to simplify code.

Change-Id: I232876910bbe4fa9719f4a0ce4a54c090faeb5ef
Signed-off-by: Matthew Bentham <Matthew.Bentham@arm.com>
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/c/VisualCompute/ComputeLibrary/+/532429
Tested-by: bsgcomp <bsgcomp@arm.com>
Reviewed-by: Pablo Tello <pablo.tello@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/9856
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Viet-Hoa Do <viet-hoa.do@arm.com>
Benchmark: Arm Jenkins <bsgcomp@arm.com>
diff --git a/src/core/utils/ActivationFunctionUtils.cpp b/src/core/utils/ActivationFunctionUtils.cpp
new file mode 100644
index 0000000..4854b8e
--- /dev/null
+++ b/src/core/utils/ActivationFunctionUtils.cpp
@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2016-2023 Arm Limited.
+ *
+ * SPDX-License-Identifier: MIT
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to
+ * deal in the Software without restriction, including without limitation the
+ * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+ * sell copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "arm_compute/core/utils/ActivationFunctionUtils.h"
+
+#include <map>
+
+namespace arm_compute
+{
+const std::string &string_from_activation_func(const ActivationFunction& act)
+{
+    static std::map<ActivationFunction, const std::string> act_map =
+    {
+        { ActivationFunction::ABS, "ABS" },
+        { ActivationFunction::LINEAR, "LINEAR" },
+        { ActivationFunction::LOGISTIC, "LOGISTIC" },
+        { ActivationFunction::RELU, "RELU" },
+        { ActivationFunction::BOUNDED_RELU, "BRELU" },
+        { ActivationFunction::LU_BOUNDED_RELU, "LU_BRELU" },
+        { ActivationFunction::LEAKY_RELU, "LRELU" },
+        { ActivationFunction::SOFT_RELU, "SRELU" },
+        { ActivationFunction::ELU, "ELU" },
+        { ActivationFunction::SQRT, "SQRT" },
+        { ActivationFunction::SQUARE, "SQUARE" },
+        { ActivationFunction::TANH, "TANH" },
+        { ActivationFunction::IDENTITY, "IDENTITY" },
+        { ActivationFunction::HARD_SWISH, "HARD_SWISH" },
+        { ActivationFunction::SWISH, "SWISH" },
+        { ActivationFunction::GELU, "GELU" }
+
+    };
+
+    return act_map[act];
+}
+
+} // namespace arm_compute