cpu/samd51: add common header file from ASF

Somehow I forgot to commit this.

cpu/sam0_common/include/vendor/samd51/include/samd51.h

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+/**
+ * \file
+ *
+ * \brief Top header file for SAMD51
+ *
+ * Copyright (c) 2019 Microchip Technology Inc.
+ *
+ * \asf_license_start
+ *
+ * \page License
+ *
+ * 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 Licence at
+ * 
+ * http://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.
+ *
+ * \asf_license_stop
+ *
+ */
+
+#ifndef _SAMD51_
+#define _SAMD51_
+
+/**
+ * \defgroup SAMD51_definitions SAMD51 Device Definitions
+ * \brief SAMD51 CMSIS Definitions.
+ */
+
+#if   defined(__SAMD51G18A__) || defined(__ATSAMD51G18A__)
+  #include "samd51g18a.h"
+#elif defined(__SAMD51G19A__) || defined(__ATSAMD51G19A__)
+  #include "samd51g19a.h"
+#elif defined(__SAMD51J18A__) || defined(__ATSAMD51J18A__)
+  #include "samd51j18a.h"
+#elif defined(__SAMD51J19A__) || defined(__ATSAMD51J19A__)
+  #include "samd51j19a.h"
+#elif defined(__SAMD51J19B__) || defined(__ATSAMD51J19B__)
+  #include "samd51j19b.h"
+#elif defined(__SAMD51J20A__) || defined(__ATSAMD51J20A__)
+  #include "samd51j20a.h"
+#elif defined(__SAMD51J20C__) || defined(__ATSAMD51J20C__)
+  #include "samd51j20c.h"
+#elif defined(__SAMD51N19A__) || defined(__ATSAMD51N19A__)
+  #include "samd51n19a.h"
+#elif defined(__SAMD51N20A__) || defined(__ATSAMD51N20A__)
+  #include "samd51n20a.h"
+#elif defined(__SAMD51P19A__) || defined(__ATSAMD51P19A__)
+  #include "samd51p19a.h"
+#elif defined(__SAMD51P20A__) || defined(__ATSAMD51P20A__)
+  #include "samd51p20a.h"
+#else
+  #error Library does not support the specified device.
+#endif
+
+#endif /* _SAMD51_ */