Pool2d changes to enable fp16 in armv8a multi_isa builds

* FP16 kernels must be moved from src/cpu/kernels/pool2d/neon/nchw/all.cpp
  to src/cpu/kernels/pool2d/neon/fp16.cpp.

* In src/cpu/kernels/pool2d/neon/list.h when we declare the kernels
  we need to remove defined(__ARM_FEATURE_FP16_VECTOR_ARITHMETIC) so that
  in std::vector<CpuPool2dKernel::PoolingKernel> available_kernels

* Partially resolves MLCE-1102

Change-Id: I000380f8eccca17e6219c4f3453980d67a2c9dd8
Signed-off-by: Pablo Marquez Tello <pablo.tello@arm.com>
Reviewed-on: https://review.mlplatform.org/c/ml/ComputeLibrary/+/10444
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/cpu/kernels/pool2d/neon/list.h b/src/cpu/kernels/pool2d/neon/list.h
index f8f458a..5db843d 100644
--- a/src/cpu/kernels/pool2d/neon/list.h
+++ b/src/cpu/kernels/pool2d/neon/list.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2021 Arm Limited.
+ * Copyright (c) 2021, 2023 Arm Limited.
  *
  * SPDX-License-Identifier: MIT
  *
@@ -21,8 +21,8 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  */
-#ifndef SRC_CORE_NEON_KERNELS_POOLING_LIST_H
-#define SRC_CORE_NEON_KERNELS_POOLING_LIST_H
+#ifndef ACL_SRC_CPU_KERNELS_POOL2D_NEON_LIST_H
+#define ACL_SRC_CPU_KERNELS_POOL2D_NEON_LIST_H
 
 #include "arm_compute/core/Types.h"
 #include "arm_compute/core/utils/misc/Traits.h"
@@ -47,11 +47,11 @@
 
 #if defined(ENABLE_NCHW_KERNELS)
 
-#if defined(__ARM_FEATURE_FP16_VECTOR_ARITHMETIC) && defined(ENABLE_FP16_KERNELS)
+#if defined(ENABLE_FP16_KERNELS)
 DECLARE_POOLING_KERNEL(pooling2_fp16_neon_nchw);
 DECLARE_POOLING_KERNEL(pooling3_fp16_neon_nchw);
 DECLARE_POOLING_KERNEL(poolingMxN_fp16_neon_nchw);
-#endif /* defined(__ARM_FEATURE_FP16_VECTOR_ARITHMETIC) && defined(ENABLE_FP16_KERNELS) */
+#endif /* defined(ENABLE_FP16_KERNELS) */
 
 DECLARE_POOLING_KERNEL(pooling2_fp32_neon_nchw);
 DECLARE_POOLING_KERNEL(pooling3_fp32_neon_nchw);
@@ -110,4 +110,4 @@
 } // namespace cpu
 } // namespace arm_compute
 
-#endif // SRC_CORE_NEON_KERNELS_POOLING_LIST_H
+#endif // ACL_SRC_CPU_KERNELS_POOL2D_NEON_LIST_H