Revert removal of header guard and addition of full license in the header

Author: lukamac

TargetLibraries/PULPOpen/inc/kernel/gemm.h

@@ -2,20 +2,11 @@
  * SPDX-FileCopyrightText: 2020 ETH Zurich and University of Bologna
  *
  * SPDX-License-Identifier: Apache-2.0
- *
- * Licensed under the Apache License, Version 2.0 (the License); you may
- * not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an AS IS BASIS, WITHOUT
- * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
  */
 
+#ifndef __DEEPLOY_MATH_GEMM_KERNEL_HEADER_
+#define __DEEPLOY_MATH_GEMM_KERNEL_HEADER_
+
 #include "DeeployPULPMath.h"
 
 void PULP_Gemm_fp32_fp32_fp32_fp32(const float32_t *__restrict__ pSrcA,