Move CPU/GPU files from Core/Runtime to the respective backend folders

Legacy structure contained two libraries core/runtime with two backends
in each.
We reduce the core/runtime libraries to a single library thus merging
the backend files

Signed-off-by: Georgios Pinitas <georgios.pinitas@arm.com>
Change-Id: I69545765fe7a730368105cdbd067d3135ec7a174
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/6155
Comments-Addressed: Arm Jenkins <bsgcomp@arm.com>
Reviewed-by: Michele Di Giorgio <michele.digiorgio@arm.com>
Tested-by: Arm Jenkins <bsgcomp@arm.com>
diff --git a/docs/contributor_guide/adding_operator.dox b/docs/contributor_guide/adding_operator.dox
index 772d436..ab17483 100644
--- a/docs/contributor_guide/adding_operator.dox
+++ b/docs/contributor_guide/adding_operator.dox
@@ -119,11 +119,11 @@
 
 The structure of the kernel .cpp file should be similar to the next ones.
 For OpenCL:
-@snippet src/core/gpu/cl/kernels/ClReshapeKernel.cpp ClReshapeKernel Kernel
+@snippet src/gpu/cl/kernels/ClReshapeKernel.cpp ClReshapeKernel Kernel
 The run will call the function defined in the .cl file.
 
 For the Arm® Neon™ backend case:
-@snippet src/core/cpu/kernels/CpuReshapeKernel.cpp NEReshapeLayerKernel Kernel
+@snippet src/cpu/kernels/CpuReshapeKernel.cpp NEReshapeLayerKernel Kernel
 
 In the Arm® Neon™ case, there is no need to add an extra file and we implement the kernel in the same NEReshapeLayerKernel.cpp file.
 If the tests are already in place, the new kernel can be tested using the existing tests by adding the configure and run of the kernel to the compute_target() in the fixture.