You can find these files in the BSP Layer at:
meta-bsp_root_name
/bsp_license_file
These optional files satisfy licensing requirements
for the BSP.
The type or types of files here can vary depending
on the licensing requirements.
For example, in the Raspberry Pi BSP all licensing
requirements are handled with the
COPYING.MIT
file.
Licensing files can be MIT, BSD, GPLv*, and so forth. These files are recommended for the BSP but are optional and totally up to the BSP developer. For information on how to maintain license compliance, see the "Maintaining Open Source License Compliance During Your Product's Lifecycle" section in the Yocto Project Development Tasks Manual.