Add missing license identifier

[bernhardmgruber]

This PR ensures that every C++ and CMake source file of LLAMA has a copyright/license header of the form:

// Copyright <year> <autor>
// SPDX-License-Identifier: <license>

This also fixes using the wrong SPDX identifier GPL-3.0-or-later in some places, where LGPL-3.0-or-later was intended, since LLAMA as a whole is licensed under LGPL as pointed out in the LICENSE file. No relicensing of any kind is performed. Just adding and correcting information where missing or wrong.

[codecov[bot]]

Codecov Report

Merging #707 (1492a53) into develop (6ee96be) will not change coverage. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #707 +/- ## ======================================== Coverage 98.78% 98.78% ======================================== Files 74 74 Lines 7157 7157 ======================================== Hits 7070 7070 Misses 87 87 ```