Add correct copyright notices

The [LICENSE](LICENSE) file just says `Copyright (c) 2020 M5Stack` which isn't right. For example [In_eSPI.h](https://github.com/m5stack/M5StickC/blob/master/src/utility/In_eSPI.h) is from [TFT_eSPI](https://github.com/Bodmer/TFT_eSPI/blob/master/license.txt) with various authors whose work is used without any attribution. I assume other files are similar.