Improve SPDX identifier coverage (#716)

* Change MIT license texts to SPDX-License-Identifier

SPDX-License-Identifier is much easier to understand and grep than
license text so use that instead.

* Change GPL exception license texts to SPDX-License-Identifier

SPDX-License-Identifier is much easier to understand and grep than
license text so use that instead.

* Change misc license texts to SPDX-License-Identifier

There are some external code in repo which are not licenses as most of
the stuff in this repo. We still want every file to have SPDX identifier
to easily grep licenses.

* Add currently used license files

Even though Bacnet-Stack is using SPDX identifiers we still need to give
those license files with source. For this reason add all license files
to license/ folder.

SPDX has also files which would make same thing but this is style which
example Linux kernel is using and it is quite clear so I choose that one
for now.

I choosed not yet bring CC-PDDC as that is not right license for those
files.

---------

Co-authored-by: Kari Argillander <kari.argillander@fidelix.com>

test/ztest/include/zephyr/test_utils.h

@@ -3,30 +3,7 @@
 /*
  *  Copyright (C) 2015 by Intel Corporation, All Rights Reserved.
  *
- *  Redistribution and use in source and binary forms, with or without
- *  modification, are permitted provided that the following conditions are met:
- *
- *    - Redistributions of source code must retain the above copyright notice,
- *     this list of conditions and the following disclaimer.
- *
- *    - Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- *
- *    - Neither the name of Intel Corporation nor the names of its contributors
- *    may be used to endorse or promote products derived from this software
- *    without specific prior written permission.
- *
- *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
- *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
- *  DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
- *  FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- *  DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
- *  SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
- *  CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
- *  OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
- *  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *  SPDX-License-Identifier: BSD-3-Clause
  */
 
 #ifndef __TEST_UTILS_H__