Make CpuActivation stateless

- Rename NEActivationLayer to CpuActivation
- Add member function to generate execution window

Partially Resolves: COMPMID-3992

Signed-off-by: Georgios Pinitas <georgios.pinitas@arm.com>
Change-Id: I4e1ae15cf456b860d3080b2fedc4dbcce7d1bb79
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/4791
Tested-by: Arm Jenkins <bsgcomp@arm.com>
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Michalis Spyrou <michalis.spyrou@arm.com>
diff --git a/arm_compute/runtime/NEON/functions/NEFloor.h b/arm_compute/runtime/NEON/functions/NEFloor.h
index 9299350..739225c 100644
--- a/arm_compute/runtime/NEON/functions/NEFloor.h
+++ b/arm_compute/runtime/NEON/functions/NEFloor.h
@@ -32,6 +32,7 @@
 
 namespace arm_compute
 {
+// Forward declarations
 class ITensor;
 class ITensorInfo;